This is an issue that can happen sometimes between our servers and the Facebook ones.
As the game is connected to Facebook, we advise to go to a PC and follow the steps below;

1. [Keep the Request list clean]
Please remember that the capacity of the Message centre is 50 requests and once you reach it no new requests can enter.
Also it's important to know that the requests expire in 24 hours and if you accept them after this time has passed you won't be able to obtain the item they contained.

In order to solve this issue we suggest the next steps:
-Enter this link: https://www.facebook.com/appcenter/requests
-Go to the Monster Legends section and click on ""Ignore all"".
-Enter Monster Legends.
-Send a gift to a friend and ask him to accept it.
-Then ask a friend to send you a gift.

2. [Clear Cache and Cookies from your browser and FlashPlayer]

Many of the loading issues can be solved with simply clearing the Cache and Cookies of your browser, as well as the Flash Player's Cache.

-Clear Cache and Cookies of your browser:
http://support.google.com/accounts/bin/answer.py?hl=en&answer=32050

-Clear Flash Player Cache:
http://forums.adobe.com/message/4278569