Not all endpoints properly support before cursors. I haven’t tested with Get Clips, but it could simply be one of the endpoints that doesn’t allow using before and the documentation could incorrectly list it as a param.
Also, if you want to get pages 1, 2, and 1 again, rather than using before you should just make the request without any cursor and it will give you page 1. Generally for most use cases, such as polling an endpoint, it’s common to just get page 1, keep using after to get as many pages as you need, then the next time you need the data you start from scratch and page through again.