Ajax error sending test mail

Hello while trying to send a test email I receive the following message:
Sending the message: Ajax Error
I have trued to stop other plugins but it didn’t help.
Here is a part the log, please advise. Thanks.

Unexpected PHP messages corrupted the Ajax response:

PostSMTP\Vendor\GuzzleHttp\Exception\RequestException Object
(
    [request:PostSMTP\Vendor\GuzzleHttp\Exception\RequestException:private] => PostSMTP\Vendor\GuzzleHttp\Psr7\Request Object
        (
            [method:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => POST
            [requestTarget:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => 
            [uri:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => PostSMTP\Vendor\GuzzleHttp\Psr7\Uri Object
                (
                    [scheme:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => https
                    [userInfo:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => 
                    [host:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => oauth2.googleapis.com
                    [port:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => 
                    [path:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => /token
                    [query:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => 
                    [fragment:PostSMTP\Vendor\GuzzleHttp\Psr7\Uri:private] => 
                )

            [headers:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => Array
                (
                    [Content-Length] => Array
                        (
                            [0] => 279
                        )

                    [User-Agent] => Array
                        (
                            [0] => GuzzleHttp/6.5.5 curl/7.70.0 PHP/7.4.9
                        )

                    [Host] => Array
                        (
                            [0] => oauth2.googleapis.com
                        )

                    [Cache-Control] => Array
                        (
                            [0] => no-store
                        )

                    [Content-Type] => Array
                        (
                            [0] => application/x-www-form-urlencoded
                        )

                )

            [headerNames:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => Array
                (
                    [content-length] => Content-Length
                    [user-agent] => User-Agent
                    [host] => Host
                    [cache-control] => Cache-Control
                    [content-type] => Content-Type
                )

            [protocol:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => 1.1
            [stream:PostSMTP\Vendor\GuzzleHttp\Psr7\Request:private] => PostSMTP\Vendor\GuzzleHttp\Psr7\Stream Object
                (
                    [stream:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => Resource id #310
                    [size:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => 279
                    [seekable:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => 1
                    [readable:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => 1
                    [writable:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => 1
                    [uri:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => php://temp
                    [customMetadata:PostSMTP\Vendor\GuzzleHttp\Psr7\Stream:private] => Array
                        (
                        )

                )

        )

    [response:PostSMTP\Vendor\GuzzleHttp\Exception\RequestException:private] => 
    [handlerContext:PostSMTP\Vendor\GuzzleHttp\Exception\RequestException:private] => Array
        (
            [errno] => 60
            [error] => SSL certificate problem: unable to get local issuer certificate
            [appconnect_time] => 0
            [url] => https://oauth2.googleapis.com/token
            [content_type] => 
            [http_code] => 0
            [header_size] => 0
            [request_size] => 0
            [filetime] => -1
            [ssl_verify_result] => 20
            [redirect_count] => 0
            [total_time] => 0.061807
            [namelookup_time] => 0.003616
            [connect_time] => 0.005414
            [pretransfer_time] => 0
            [size_upload] => 0
            [size_download] => 0
            [speed_download] => 0
            [speed_upload] => 0
            [download_content_length] => -1
            [upload_content_length] => -1
            [starttransfer_time] => 0
            [redirect_time] => 0
            [redirect_url] => 
            [primary_ip] => 142.251.142.202
            [certinfo] => Array
                (
                )

            [primary_port] => 443
            [local_ip] => 91.202.171.6
            [local_port] => 53518
            [http_version] => 0
            [protocol] => 2
            [ssl_verifyresult] => 0
            [scheme] => HTTPS
            [appconnect_time_us] => 0
            [connect_time_us] => 5414
            [namelookup_time_us] => 3616
            [pretransfer_time_us] => 0
            [redirect_time_us] => 0
            [starttransfer_time_us] => 0
            [total_time_us] => 61807
            [curl_version] => 7.70.0
        )

    [message:protected] => cURL error 60: SSL certificate problem: unable to get local issuer certificate (see https://curl.haxx.se/libcurl/c/libcurl-errors.html)
    [string:Exception:private] => 
    [code:protected] => 0
    [file:protected] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\CurlFactory.php
    [line:protected] => 132
    [trace:Exception:private] => Array
        (
            [0] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\CurlFactory.php
                    [line] => 116
                    [function] => createRejection
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\CurlFactory
                    [type] => ::
                )

            [1] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\CurlFactory.php
                    [line] => 88
                    [function] => finishError
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\CurlFactory
                    [type] => ::
                )

            [2] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\CurlHandler.php
                    [line] => 37
                    [function] => finish
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\CurlFactory
                    [type] => ::
                )

            [3] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\Proxy.php
                    [line] => 24
                    [function] => __invoke
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\CurlHandler
                    [type] => ->
                )

            [4] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Handler\Proxy.php
                    [line] => 43
                    [function] => PostSMTP\Vendor\GuzzleHttp\Handler\{closure}
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\Proxy
                    [type] => ::
                )

            [5] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\PrepareBodyMiddleware.php
                    [line] => 56
                    [function] => PostSMTP\Vendor\GuzzleHttp\Handler\{closure}
                    [class] => PostSMTP\Vendor\GuzzleHttp\Handler\Proxy
                    [type] => ::
                )

            [6] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Middleware.php
                    [line] => 29
                    [function] => __invoke
                    [class] => PostSMTP\Vendor\GuzzleHttp\PrepareBodyMiddleware
                    [type] => ->
                )

            [7] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\RedirectMiddleware.php
                    [line] => 55
                    [function] => PostSMTP\Vendor\GuzzleHttp\{closure}
                    [class] => PostSMTP\Vendor\GuzzleHttp\Middleware
                    [type] => ::
                )

            [8] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Middleware.php
                    [line] => 53
                    [function] => __invoke
                    [class] => PostSMTP\Vendor\GuzzleHttp\RedirectMiddleware
                    [type] => ->
                )

            [9] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\HandlerStack.php
                    [line] => 64
                    [function] => PostSMTP\Vendor\GuzzleHttp\{closure}
                    [class] => PostSMTP\Vendor\GuzzleHttp\Middleware
                    [type] => ::
                )

            [10] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Client.php
                    [line] => 302
                    [function] => __invoke
                    [class] => PostSMTP\Vendor\GuzzleHttp\HandlerStack
                    [type] => ->
                )

            [11] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Client.php
                    [line] => 101
                    [function] => transfer
                    [class] => PostSMTP\Vendor\GuzzleHttp\Client
                    [type] => ->
                )

            [12] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\guzzlehttp\guzzle\src\Client.php
                    [line] => 115
                    [function] => sendAsync
                    [class] => PostSMTP\Vendor\GuzzleHttp\Client
                    [type] => ->
                )

            [13] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\google\auth\src\HttpHandler\Guzzle6HttpHandler.php
                    [line] => 45
                    [function] => send
                    [class] => PostSMTP\Vendor\GuzzleHttp\Client
                    [type] => ->
                )

            [14] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\google\auth\src\OAuth2.php
                    [line] => 443
                    [function] => __invoke
                    [class] => PostSMTP\Vendor\Google\Auth\HttpHandler\Guzzle6HttpHandler
                    [type] => ->
                )

            [15] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\libs\vendor_prefixed\google\apiclient\src\Client.php
                    [line] => 287
                    [function] => fetchAuthToken
                    [class] => PostSMTP\Vendor\Google\Auth\OAuth2
                    [type] => ->
                )

            [16] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\PostmanGmailApiModuleTransport.php
                    [line] => 100
                    [function] => fetchAccessTokenWithRefreshToken
                    [class] => PostSMTP\Vendor\Google\Client
                    [type] => ->
                )

            [17] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Mail\PostmanZendMailEngine.php
                    [line] => 190
                    [function] => createZendMailTransport
                    [class] => PostmanGmailApiModuleTransport
                    [type] => ->
                )

            [18] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\PostmanWpMail.php
                    [line] => 236
                    [function] => send
                    [class] => PostmanZendMailEngine
                    [type] => ->
                )

            [19] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\PostmanWpMail.php
                    [line] => 60
                    [function] => sendMessage
                    [class] => PostmanWpMail
                    [type] => ->
                )

            [20] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\PostmanWpMailBinder.php
                    [line] => 121
                    [function] => send
                    [class] => PostmanWpMail
                    [type] => ->
                )

            [21] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-content\plugins\post-smtp\Postman\Postman-Send-Test-Email\PostmanSendTestEmailController.php
                    [line] => 278
                    [function] => wp_mail
                )

            [22] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-includes\class-wp-hook.php
                    [line] => 308
                    [function] => sendTestEmailViaAjax
                    [class] => PostmanSendTestEmailAjaxController
                    [type] => ->
                )

            [23] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-includes\class-wp-hook.php
                    [line] => 332
                    [function] => apply_filters
                    [class] => WP_Hook
                    [type] => ->
                )

            [24] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-includes\plugin.php
                    [line] => 517
                    [function] => do_action
                    [class] => WP_Hook
                    [type] => ->
                )

            [25] => Array
                (
                    [file] => C:\inetpub\wwwroot\TevalifeWordpress\wp-admin\admin-ajax.php
                    [line] => 188
                    [function] => do_action
                )

        )

    [previous:Exception:private] => 
)