To separate them from the path between you, which is your second question and the one that decides who you are even talking to:
Test from somewhere else. Run the same call from a different network and a different region — a cloud shell, a VPS, your laptop on a phone hotspot. If it fails everywhere, it is them. If it only fails from your infrastructure, the problem is in your path or your egress, and no amount of pushing on their support will move it. This takes five minutes and it is the highest-value thing in this thread.
Look at where in the request it dies. A timeout during connection establishment points at the network path. A timeout after the request was accepted but before a response points at their processing. Curl's timing breakdown gives you this directly — DNS, connect, TLS, first byte — and the shape of it is genuinely diagnostic.
Check DNS resolution. Compare what your resolver returns against a public resolver. Getting a different or stale set of addresses is a real and surprisingly common cause of "a fraction of requests fail", because some of your connections are going somewhere they should not.
Rule out your own retry behaviour. A fifth failing with some 502s can also be you retrying into a pool that is already saturated. Check whether the failure rate correlates with your own request volume, because if it does, part of this is yours.