I have finally succeeded in obtaining a certificate for www.doldari.com.
It seems there was an issue with the port forwarding setup. Previously, I had only configured TCP for ports 80 and 433 on the iptime router. This time, I also set up UDP, and I believe this is why the certificate issuance was successful.
Thank you to everyone who helped and showed interest.
In particular, I was able to identify the networking issue by first running a test on Let's Debug, as suggested by Bruce5051.