HTTPS Site problem: Blocked loading mixed active content

my site running ssl from cloudflare.
when i submit the form, i get this error in console:

Blocked loading mixed active content “http://(removed)/wp-admin/admin-ajax.php?callback=jQuery112408010996233335644_1467234826583”

tried to add this line to widget_nl.php
$iframeCssUrl = str_replace(“http:”, “”,$iframeCssUrl);

nothing changed.

any solution for https sites?

https://ww.wp.xz.cn/plugins/wysija-newsletters/