I searched the title but the only reference I found applied to unsubscribing whereas I get this message no matter what I provide for the Name and Email on the subscription form. The subscription form then disappears after three seconds, or so.

I've checked my settings but everything looks okay to me. Is this something that's familiar to someone?

Did you set "Allow user data modifications without identification" parameter to Yes in AcyMailing Configuration, under the Subscription tab?

I failed to understand what "Allow subscriber data modifications without authentication" actually means. the language is not direct. But yes, that did the trick. Nonetheless, I finally focused on the fact that the entry level system has no bounce support so it's pointless for me to continue with this system. But thanks for your help. I appreciate it.