Since REST is stateless by design, there is no way to roll back a transaction. A possible way is to create certain endpoints/methods designated to validating a request. Let's say that you want to call UploadDocument -- there could be a ValidateUploadDocument. If the latter returns anything else than 200, you just won't call the former.

In your case:

1. Call C1Validate, C2Validate, and C3Validate
2. If all calls return status code 200, call C1, C2, and C3.

Naturally, this could require changing your services in the first place. Another potentially less elegant way is to use DELETE for C1 and C2 if C3 fails (if DELETE methods are available).

What you described here is called 2-phase commit protocol.

That's a standard practice for distributed databases, but could be applied in your situation as well.

Please, read more about it on, for example, wikipedia. The only requirement is that you should have access to external services to change it (add new operations)