What is the ruling on using paid codes provided for free by another website?

There is no objection to allowing advertising companies to place their ads in applications, as long as they are free of forbidden content, and it is permissible to profit from them.

As for dealing with websites that provide codes: if it is highly probable that they obtain them through piracy, then it is not permissible to benefit from them, because copyrights and intellectual property rights are protected by Islamic law. However, if these codes are created by the websites themselves or if their owners have permitted their publication, then there is no objection to taking them.