Couldn’t connect to the MailPoet server

Hello, We have a site that got upgraded to PHP 7.3, and it seems that we need to switch to MailPoet 3. I just installed it, but there are issues between MailPoet and how the server is set up. I can’t save any settings or do the automatic update to MailPoet 3 — I just get the error message: “Sorry, but we couldn’t connect to the MailPoet server. Please refresh the web page and try again.” The site is using a reverse proxy and I have the site set up via wp-config not to search for automatic updates. Why should the plugin be trying to connect to the MailPoet server at all? I am just trying to save settings. Please advise, as otherwise we will need to switch mailers. Thanks.