Depending on where you live they can call it different things. Flank steak and Flap meat, skirt steak and flat iron steaks are very similar. Often I can get flap meat for half of what flank steak costs, I talked to the butcher in a few stores near me and they say all those cuts are similar and great for marinading.
Also here in Calif. Tri-tip is popular but I can not get it when I’m in NJ the butchers there say they don’t sell it, but it’s been popular in Ca for many years.
When in doubt ask the butcher, but just looking at steak you can tell how much marbling is in it and the texture. Like flank and flap, they look similar.

In your list of ingredients you say to use flap meat, did you mean flank?