Allow user to create database in a virtual domain

For that to work, you'd want to make sure the "MySQL Database Enabled" feature is checked in "Edit Virtual Server".

Additionally, look in Administration Options -> Edit Owner Limits, and make sure they haven't reached the database limit set in "Maximum allowed databases".

And lastly, on that same screen, look in "Allowed capabilities and features", and make sure that "Can manage databases" is checked.

Ref:

https://www.virtualmin.com/node/18161