There are two most common reasons why sending crypto might fail:
We impose limits to the amount of crypto that can be withdrawn on a daily/monthly basis. This will be shown to you in the app when you try to withdraw.
We perform checks on addresses added at multiple stages. When you first add the address, and when you try to make a withdrawal. If the address has been flagged after you added it, you will not be able to execute a withdrawal and your address will be disabled. However, you will still be able to see it and won't be able to remove it.