I don’t know if the rules are different in your part of the world, but when we bought our house many years ago, we wanted to make a one-sided agreement with our new neighbors and our laywer told us it wouldn’t stand up.
Here are the details. When we looked at the survey before closing the deal, we found that our neighbors’ driveway overlapped a little onto our property. We didn’t care about that, but we did care that there be no question about where the property line was. In the USA, there is something called the “right of adverse possession:” If you use someone else’s property for long enough, and the owner knows about it and doesn’t object, it becomes yours.
So we wanted to be sure that the strip of land under our neighbor’s driveway didn’t become their property. The reason was that we might want to add onto the house someday, and there were rules about how far an addition had to be from the property line. Move the line, and you change the size of the allowable addition.
Anyway, we wanted to tell the people who were selling us the house that before we would buy it, they would have to get an agreement from their neighbors (soon to be our neighbors, we hoped) that they acknkowledged that they did not own that strip of land.
Our lawyer told us that such an agreement was not legitimate. In order for a contract to be enforceable in court, at least in New Jersey in 1984 (which was when we bought our house), each party to the contract had to gain something. So in order for their acknowledgment to be legitimate, we had to give them something in exchange for it.
So we changed the contract: In exchange for their agreeing that we owned that strip of land, and that we had the right to remove that part of their driveway any time we wanted, we agreed to give them 60 days’ notice if we ever decided to remove that part of their driveway. This way, we both gained something from the deal.
So…If you sign a contract that gives someone else the right to use a piece of music you wrote, and you don’t get anything in return, it just might be that the contract is not binding. If you care, I would suggest you check with a lawyer who knows what the rules are wherever the contract is intended to be in force.