Resolved webmail only in https:

[CobraArbok]

Another issue related to mail.

If I call "webmail.mydomain.tld", then in Roundcube I get an error about login or "Request not valide".
If I call "https://webmail.mydomain.tld" I able to login.

The "mydomain.tld" is secured with Let's encrypt.
Also mail.mydomain.tld and webmail.mydomain.tld with the same certificate of mydomain.tld.
All domains have enabled the option "Permanent SEO-safe 301 redirect from HTTP to HTTPS"

Where am I wrong?

==== Update ====
I removed webmail subdomain