Webdav access to Synology from iOS fails with 3.08 but works fine with 2.51

lbmh

We get the following message

Failed secure connection

An SSL error has occurred and a
secure connection with the server
can't be established. If you are using a
self-signed certificate or a proxy,
check that you have installed the profile
on your device.

With 3.0.8 whereas everything is fine when accessing the same Webdav synology.me URL with 2.51 on antoher device.

Both self-signed & let's encrypt certificates from the Synology NAS have been installed, to no avail.

Does anyone has an idea on how to get and install BoxCryptor 2.51 ?

Thanks in advance !