Error: Invalid argument & Headers already sent

I have used this plugin a lot on client websites. When I went to install it on one today I got the following error and warning:

Warning: Invalid argument supplied for foreach() in /home/name/public_html/website.com/site/wp-content/plugins/social-networks-auto-poster-facebook-twitter-g/inc/nxs_snap_class.php on line 37

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/name/public_html/website.com/site/wp-content/plugins/social-networks-auto-poster-facebook-twitter-g/inc/nxs_snap_class.php:37) in /home/hame/public_html/website.com/site/wp-content/plugins/custom-sidebars/inc/class-custom-sidebars-explain.php on line 55

The plugin generated 488 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.

I deactivated and removed the Custom Sidebars plugin but when I activated SNAP I then got the same Invalid Argument error and the 488 character message.

I then deactivated all plugins and then reactivated SNAP but got the same error. As I use the same parent theme on all my WP websites I’ve done in the last year and have had no other problems with your plugin, I doubt it is a theme conflict.

Do you have any insights into why this could be happening?

https://ww.wp.xz.cn/plugins/social-networks-auto-poster-facebook-twitter-g/