A monthly payment for what exactly? Are you paying for your purchase over time?
That is the idea to pay back our up front payment. My partners indicated they didn't think we needed to pay taxes until the the initial payments were covered. While they have more experience with businesses, I wanted to try and make sure. Any advice is always welcome. Thanks
income from your part ownership is income and you have to report it.
the amount you invested does not matter until you sell your ownership.
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.
@biglebowski1128 is correct. I also recommend that you seek out local legal advice. This might actually be a loan, rather than an investment. Whatever it is, it needs to be in writing.