GroupTalk users with bluetooth RSM or PTT button should NOT upgrade their iPhone or iPad to iOS 12.4 yet
The iOS 12.4 update from Apple includes a limitation/bug that requires the GroupTalk app to be visible on the screen of the iPhone or iPad to be able to send Push to Talk messages.
GroupTalk users with bluetooth Remote Speaker Microphones or Bluetooth PTT buttons will NOT be able to activate PTT from these accessories when the GroupTalk app is in the “background” (not visible on the screen) on their iPhone or iPad if iOS 12.4 is installed. If you use GroupTalk with PTT accessories, you should NOT upgrade to iOS 12.4.
In order to receive incoming PTT messages on devices with iOS 12.4 it is required that you update the GroupTalk for iPhone app to version 3.3.6 or later version.