Can't connect to homeserver Matrix acccount with Cinny

[croulibri]

Describe the bug

Can't connect to my home server Synapse account (installed with Yunohost) with this Cinny app installed on specific subdomain.

Context

Server on small computer at home.
YunoHost 12.0.9.2
Cinny 4.2.3~ynh1

Steps to reproduce

I connect to the specific domain of my Cinny install.
On the login page, I select my home server on the list.

I am proposed to connect through SSO with ''Continue with SSO"

I arrive at the SSO page of my homeserveur.
I enter ID and passwords, click on "connexion".

Nothing happens.

Expected behavior

I am redirected to Cinny web app and have access to my Matrix account.