wms

Hi Everybody! I'm trying to add a WMS layer to my device. It's a password secured Hungarian forestry map. It has been working for years. Now I get the message: "We coundn't estabilish a sescure connection to the map server because its security certificate insn't trusted by your device. This can happen if the certificate is self-signed or from an unrecognized provider." I have an old mobile, with Android 11. Is it too old? With a newer one it is still working. Do you have any idea to solve this problem? Thank's!