Hello Muzikman69,
Thanks for visiting Apple Support Communities. We understand that you're having an issue opening the Messenger+ app from Verizon as it closes when launching. Let's see if a particular window is causing this to happen by holding the Shift key on your keyboard while opening the app. This causes the app to forget the windows that were last open. If the behavior continues, these steps may help: If an app freezes or quits unexpectedly on Mac
If you're still having an issue, let's help to narrow our focus by testing this in safe mode and a new user account. Here's a guide on safe mode and the steps to take if it does or does not happen there: How to use safe mode on your Mac
If the issue continues after those steps, create a new user account to see if it happens there too. This will let us know if the issue is system-wide or only within your account: Set up users, guests, and groups on Mac
Keep us posted.
Take care.