Alexey - Just an update that after recompiling the app, I can't get it to work with iOS 13. Search is working now but when I go to select a GIF and insert it, it just spins trying to load or I get a little empty square box which is also what appears in the chat. I'm having the same problem with mobile web on iOS 13.
Android is working well both in the native app and in mobile web
after updating the messenger just get an giphy api beta key and put it in the text box of messenger's related box in studio. then when you write a message in messenger the giphy tab will be seen near file upload tab.