Thank you @lgaetz for being as ever FreePBX definitive, my solutions have always been "off the reservation " ( which I didn’t want to post.)
@emirbesic, well done!! You earned your fishing license 
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Just as a teaser if you like mqtt but don’t have a Pi . . .
Can easily replace a few hundred bucks worth of “Tried and true” solutions that are limited to SIP messaging.
JM2CWAE