Sending an ACME HTTP validation request to gmubnt.co.uk results in an unacceptable redirect. This is most likely a misconfiguration of your web server or your web application.
Bad port number provided when fetching https://gmubnt.co.uk:18843/.well-known/acme-challenge/letsdebug-test: 18843
Trace:
@0ms: Making a request to http://gmubnt.co.uk/.well-known/acme-challenge/letsdebug-test (using initial IP 208.167.245.8)
@0ms: Dialing 208.167.245.8
@21ms: Server response: HTTP 308 Permanent Redirect
@21ms: Received redirect to https://gmubnt.co.uk:18843/.well-known/acme-challenge/letsdebug-test
A test authorization for gmubnt.co.uk to the Let's Encrypt staging service has revealed issues that may prevent any certificate for this domain being issued.
208.167.245.8: Fetching https://gmubnt.co.uk:18843/.well-known/acme-challenge/eCVCGQ_ydUa3uwjM2ClE4qvjL4N7Nol87hbe1GMNwoQ: Invalid port in redirect target. Only ports 80 and 443 are supported, not 18843