How is the restaurant organized? C Corporation, S Corporation, Partnership? If it's one of the latter two, you should receive a K-1 with your share of the restaurant's income on it. This is NOT the same as the payments you receive.
If the payments are repayments of a loan you made, some of it may be interest, in which case you should receive a 1099-INT form.
What you're being paid for and the restaurant's legal entity status are key here. You need to talk to the people in charge.
