I don’t quite follow. Are you duplicating the App:Sales sheet, because that sheet should not be viewable in the data tab, since it a special Glide Only sheet. Can you show screenshots of the relation in the data tab? I assume the relation is using SKU. Then you have a lookup column to get an array list of emails related to that SKU. You didn’t indicate what screen you are on. Are you on the restaurant details screen? Are you trying to get a list of people that purchased a booking at that restaurant?
Filtering by signed in user won’t work on columns that have multiple emails separated by a space. It has to be an array of emails within glide.
It’s hard to answer this without knowing how your app and data looks or works.