I generate newsletters twice a year and between the last issue (July 2019) and the most recent one (December 2019), there seems to have been many changes on WP and Newsletter plugin. It seems that that I was experiencing difficulties with the update plug-in from newsletter.
This has since been fixed after following the instructions, but since then, it seems that sending messages have not been successful.
I get the following error message
Last test failed with error “Function create_function() is deprecated”.
Read more to solve your issues, if any.
I haven’t been able to find anything else from the forum with this reported error message.
Is there something that can be done with the WP or with the server?