I installed Message+ from play store on a older device that is on Android 4.2.2.
Google play and Services are up to date.
The Message+ app installed. Allowed me to configure it. The system sent me a code, which I entered, and it was accepted.
Then, When it goes to sync the messages, it just sits there,, and there is a little ! point in the small symble that shows it is syncing the data, if I touch it, it pops up and tells me that it can not reach the internet. It will not send or receive messages. When trying to send one, it sits and says sending. .
Are you trying to install the application on an older deactivated phone which isn't your main device on your phone line?
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.