Oh, and one more thing: if you have tailscale or another vpn solution on your system, that likely cannot be running simultaneously with the Fly wireguard tunnel. Try turning off tailscale/other vpns and then stop and restart the Fly wireguard tunnel, and see if you’re able to access your database.
If tailscale/another vpn support split tunnels, you may be able to run those simultaneously with the Fly wireguard tunnel. That’s a more advanced setup.