Your teens first few contracts are great opportunities to teach. Take the opportunity to read through your teens first few contracts with them, line by line.
It may be a cell phone contract, car loan and yes, its boring but super important.
Ensure that they read and understand all the information and the fine print. The interest rate. Late fees. Overages. Etc.
Hopefully you have discussed and made your teen aware that this new responsibility is important and can affect their credit.
Make sure they can afford this new purchase too, its not a right, its a privilege.