The easiest way to check if the terminal has been successfully paired is to see if the splash screen is being displayed.
If this is the first time the terminal has been paired then it should show the default splash screen (the blue patterned background).
If the terminal has been paired before then it should show the branded splash screen.
Another way to check if the terminal has been successfully paired is to check the Payment Portal.
If the device has not been paired, or needs to be repaired, it can be done so here: