SSL certificate for xmpp-upload

[guilg]

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My YunoHost server

Hardware: VPS bought online (ARM)
YunoHost version: 3.8.2.2
I have access to my server : Through SSH | through the webadmin
Are you in a special context or did you perform some particular tweaking on your YunoHost instance ? : no

Description of my issue

Hey there, I have an issue sending file with XMPP. It seems there were some problems that were fixed quite recently, but now I have a certificate issue. From my understanding, now the files are sent through xmpp-upload.domain.tld.
Depending on the client, it either display some spooky message because the certificate is not correct (on Conversations for Android), or fail to send the message without explanation (Dino on Linux).
When visiting xmpp-upload.domain.tld with Firefox, it refuses to connect because of HSTS with error code “SSL_ERROR_BAD_CERT_DOMAIN”.
I think I just need to sign a certificate for xmpp-upload.domain.tld with Let’s Encrypt, as mentionned here. But I have no idea how to do that. I thought to add the domain with the Yunohost web admin to get a LE certificate, but logically it is not allowed to use this subdomain.
I guess my question can be summed up :

TL;DR : how to sign with Let’s Encrypt a subdomain that is not registered in the Yunohost web admin ?

Cheers,
Guillaume

[Aleks]

If you added the DNS configuration for xmpp-upload recently, you should just force-renew the certificate for your domain.tld and it will contain an “alternative name” which will be xmpp-upload.domain.tld and will be automatically used by Yunohost etc.

Just go to the webadmin in Domains > domain.tld > SSL certificate > Force the renewal of the current cert

[guilg]

This was it, during signing it detected xmpp-upload and it is signed now, no certificates problem anymore !
Now, images can be sent but I have an issue sending pdf, saying it is not allowed but I think I saw a fix for that somewhere.
Thanks pour ta réactivité en tout cas