Can send mail but cant receive using Mailgun and Google CloudDNS

Kindly I need help.

Have tried all i can for days but simply cant figure out what the problem is:

Running Virtualmin on GCP, using Google CloudDNS and Mailgun (owing to GCP limitation to using 3rd party mailing service). Successfully configured Mailgun to send mails, working fine.

Issue is cant receive mail.

Mailgun is NOT configured to receive mail.

checked /var/log/maillog, but found nothing relating to incoming mail.