It’s very possible I was missing something else so it didn’t work for me. But I dug over the internet for this and everywhere in thousands of threads/forums I read all the same - the [macro-…] context/thing should execute when dialing out through a trunk (SIP/Chan_sip). It didn’t. Not in the FULL log, neither in outbound headers I could see any header I was “adding”.
The version is mentioned in the first post - 15.0.16.38. Asterisk was the newest possible when I installed FPBX half a year ago, maybe v15 or so.