Seems like the CA (Certificate Authority) is not registered correctly. Have you tried executing step 2 again?
Azure apim selfhosted gateway certificate update issue.

Vamsikrishna Garimella (Contractor)
1
Reputation point
We have updated the self-hosted gateway with a new certificate as part of certificate renewal process.
Also implemented below steps
- Add a certificate .pfx file to your API Management instance.
- Use the Gateway Certificate Authority - Create Or Update REST API to associate the certificate with the self-managed gateway.
but still the gateway endpoint is showing wrong CN=test.api.net
Please advise ..
thanks.