Based on the redirect it looks like your Moodle server is redirecting https requests to http. Do you have SSL enabled on your Moodle server? Does it have a valid SSL certificate?
The first thing to check with the CA store on your server is that the default certificates are installed. If not, you should install the ca-certificates package ("sudo apt install ca-certificates").
Installation
LTI-Advanced_Grading - Can't connect to Moodle (certificate verify failed)
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