Unfortunately that panel label seems to preclude your tandem breaker.



The type "MT" (tandem) is not on the list of approved breaker types.

It probably won't burn your house down but it is not legal.

That would appear to be the case. Ok no big deal. I actually used a twin breaker to re-arrange some breakers in my panel to accommodate putting a 30A backfed generator inlet on the top right.

I actually have plenty of spaces left in my panel, but one of the 15A circuits in the panel would not reach to the new spot of the breaker, so to avoid extending it with another wire and wire nut, I just used a twin.