There may be several reasons why you may not be able to visit other zoos:

1. To visit other players zoos make sure you have the last update of the game. You can download the last update in the Play Store.
2. Check that your internet connection is working properly

If your issue still persist please contact the support team with the following information:

• Player ID (in your game settings → gear button in the right upper corner) 
• Version of the game
• Device model