Why Is a Message Displayed Indicating that the Certificate Chain Is Incomplete When I Configure HTTPS?

Perform the following operations to locate and rectify the fault:

Check whether the certificate chain is complete, whether the certificate is added in the format as required, whether all certificates are typed, and whether the certificate sequence is correct.

Ensure that the content of the certificate chain is pasted right below the content of the server certificate.

If the certificate chain is incomplete, complete the certificate chain by referring to How Do I Fix an Incomplete SSL Certificate Chain?