Is it legal to provide unofficial API?

I'm the founder of [redacted], an unofficial TikTok API. It started as a small side project, but now it has been growing quickly and we even have clients from Fortune-500 companies.

The next step is registration as a corporate, fund-raising, hiring, and some other stuff that are necessary for a company to grow.

But I'm not sure if that's legal or what kind of troubles we will have from TikTok.

So far, we have only been contacted by TikTok representatives for a trademark issue, though they were helpful and we fixed the issue quickly.