@fabgan
It seems to ....
A little while ago from the control panel of my hosting I deactivated the SSL certificate. The previous problem seems to be solved but in the same module after clicking on the send message button the following screen appears that I attach to the post.
For every message you try to send, the error appears:
"The file you are trying to upload does not have a valid extension".
I want to clarify that I'm not trying to upload any files.
The same error appears if you try to upload any file, pdf, doc, txt, etc ..