While signing a certificate for a new OpenVPN user, I received the following error message which stops the whole process (exit code 1)

Certificate is to be certified until Nov 6 08:53:05 2023 GMT (3650 days)
Sign the certificate? [y/n]:y
failed to update database
TXT_DB error number 2

Problem:
Because you have generated your own self signed certificate with the same CN (Common Name) information that the CA certificate that you’ve generated before.

Enter another Common Name.