I was able to make successful calls using the API but when I make multiple calls I usually get a Cancelled request in return. It's always after the 10th call, that's why I wondered if there is such a limit. I didn't find any information on the docs and I didn't find a reason to why I get the Cancelled error on the API call, could anyone clarify this for me or at least point to where I could get more information about this?
There is a usage quota for SafetyNet Attestation, that applies both to a maximum amount of requests per day, and also to a maximum amount of requests in a small amount of time (seconds).
In principle, the attestation status of a device is very unlikely to change multiple times in a very small amount of time (rooting and stuff takes time), so you shouldn't call the API repeatedly.
Also, Attestation is computationally and network intensive, so you really shouldn't call it repeatedly.
Timing the calls to the Attestation API is not something written in stone, but as a good rule of thumb, you should aim to call it at most a handful of times per day, and even that might be excessive.