[Solved] How to fix it?

[longthor]

[wolstech]

You need to install an SSL certificate. Assuming your domain's DNS is configured correctly and you're not using something that can break domain validation (like Cloudflare with strict SSL mode enabled), Plesk should actually fix this on its own. You can go into the SSL options and issue a certificate from let's encrypt to fix it more quickly.

Once you install a valid certificate, it should start working properly within two hours.

[longthor]

Ok, many thanks — it’s working for now.