OS X Mojave Message+ app does not work

I have tried to use the Message+ app on OS X Mojave with no luck.  The app crashes if you choose File|About.  When I enable my account, any message I try to send just gets stuck on "sending" and never goes out nor to incoming messages show up in the app.  I have tried removing references to the app in KeyChain Access and re-installing several times.   I know everything else is correct (except this OS/Client combination) because the app works fine on my phones and on my Windows PC.  So, it does seem to be related to OS X.  Any message I try to send just looks like this and the status never changes.

Screen Shot 2018-11-05 at 7.18.38 AM.png

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