App Platform does not support connecting to DigitalOcean Managed Databases during the build process if the database has trusted sources enabled. This is because the app’s network configuration information can only be provided to the database’s trusted sources list after the app has been built.
This limitation is by design.
As a workaround, you can temporarily disable trusted sources for your app. However, we recommend not connecting your database to your app at build time. This keeps the build process self-contained and independent of external services that might otherwise cause the build to fail.