Hello friends!
After many days I managed to find the problem and solve the error.
I checked the server logs and identified error code 44 in plesk that is hosted on AWS.
I commented on two lines in the file:
/etc/httpd/conf.d/mod_security.conf:
Comment security rule which causes the issue in:
# grep 'MULTIPART_UNMATCHED_BOUNDARY' /etc/httpd/conf.d/mod_security.conf
#SecRule MULTIPART_UNMATCHED_BOUNDARY "! @Eq 0" "id: '200003', phase: 2, t: none, log, deny, status: 44, msg: 'Multipart parser detected a possible unmatched boundary'
# service httpd restart
https://support.plesk.com/hc/en-us/articles/213961065-Cannot-attach-files-in-Horde-ModSecurity-Access-denied-with-code-44
