Hi@KateTT,
Based on the issue you mentioned, you want to create a Sandbox environment with the current license.
Look at the picture shown above, your current Per App Plan is simply not enough. So if you’re using just the Per App Plans, you at least need around 20 licenses to create a database for a sandbox environment as 20 licenses × 50 MB is around 1 GB required CDS storage.
In a word, no matter what type of environment, you need to consume at least 1GB of capacity.
If you have to create an app in PowerApps, purchase more licenses.
Best Regards,
Qi Qiao