From what OS did you get this error is it from IOS or Android?
It looks like a connection issue. Are you sure that you are not using a fake green wallet?
If you sure that you are using the legit wallet try to update the app and restart the device on IOS. For Android try to clear the cache of that app and reboot the device(Note green wallet from Android is buggy).
If you don't have any funds yet I suggest you switch to other wallets like BRD or Mycelium for IOS and Electrum or Mycelium for Android OS.
yes it's ios. Thanks.
And could u tell me the reason for not using the green?
I'm using Green wallet on Mac, no issues, however, I haven't try the mobile version. His not telling you to not use Green, what @BitMaxz is suggesting is to try other wallet that is more stable on IOS like Bread or Mycelium. You don't want to stick to one wallet, there are a lot of wallet out there, you might want to try it as well.