Note that the smichoot form, “mouth of: is פי pee. This is in the Torah service:
V’zot haTorah asher sar Moshe lifnei b’nei Yisrael al pi Adonai b’yad Moshe”
This (is) the Torah which Moses placed before the children of Israel by the mouth of HaShem upon the hand of Moses.
This word sounds like “pay”, so to remember it: “We have to pay before we can go through the entrance to the show.”
Or perhaps it is a cave tour? “We have to pay before we can go through the mouth of the cave.”
Or perhaps the premier performance? “We have to pay before we can go to the opening of the Opera!”
Oh, my, I think my brain was working overtime with this one!