Emoji reactions are not part of #SMS spec.

All it is, is a msg in the form:

😉 to "Original msg"

Receiving app spies that format, matches the text with original msg, puts the emoji on the lower corner of the msg

I know because my #foss msg app doesnt support them and so I just copied someone else's reaction and sent it back and it showed on their screen as a reaction.

Simple. Why oh why dont all foss sms apps support this? None of them seem to...

It is a hack but it is a useful hack.