Why is my iOS device automatically opening another app instead of BitPay's wallet for bitcoin transactions?

iOS randomly picks between the applications which can handle a given type of URI (like Bitcoin URIs) and will keep choosing that application after that point.

You can fix this issue by uninstalling the app selected by your phone. If you want to re-install the app later, iOS will (usually) pick the first app installed – in this case, the BitPay wallet app

Learn more about this URI issue.