Had an issue recently with Sendy returning a server error after trying to save a campaign. I eventually worked out it was something to do with the plain text version code. I’ve now worked out it was a link, setup in the HTML version but with no URL added.
In the plain text version the code was <a href="">link</a>.
once I added the URL I stopped getting the server error page.
So, if anyone experiences similar, you know what to check for!
Putting this here incase anyone searches and finds it.