Just recording this, as I was only able to find an unconfirmed hint on a forum.
You need to open up port 9933 (not sure whether TCP or UDP … I opened both, and didn’t bother going back to experiment) on your firewall/router in order to enable the Big Blue Bubble iOS game My Singing Monsters to connect to its server. Otherwise, you’ll get the “Failed to Connect to Server” error from the game.
Hope this helps someone …
It helped us in our school district, so thank you!
Tcp/9933 and destination is amazon aws range.