Schlissle Challa Minhag Explained

One year the shabbos after pesach, I was at someone's house, and they had baked a key in their challa. They told me it's a called schlissle challa and is (like so many other things) a segula for parnossa or something.

Last shabbos I figured out a rationale for this minhag (but not the connection to parnassa), why bake a key into the challa on the shabbos after pesach. First of all, it depends on having the minhag to give your key to the goy to whom you sell your chametz when you sell your chametz. Once you have that minhag, it makes sense that on the shabbos after Pesach, when you've bought your chametz back from the goy, you bake that key in a challa, to demonstrate that you again own your chametz (represented by the challa). Maybe the parnassa thing comes from the fact this key was used in a business transaction (the sale of the chametz) and you successfully completed that deal, so you hope your successful streak continues.