If you get intermittent mollie.api.error.RequestError with ReadTimeoutError against api.mollie.com, especially on Azure where the first attempt fails and the retry succeeds, the culprit is idle connection timeouts on the Azure side silently killing reused connections. The fix the maintainers recommend is to stop reusing connections: instantiate a new Client for each request (client = Client(timeout=(2, 20)); client.set_api_key(key)) instead of sharing one long-lived client. The original reporter confirmed this resolved it, and it had already worked for multiple other Azure users. Note the v3 client added its own timeout and retry mechanism, so if you just upgraded from v2 this behavior change can be the thing that surfaces the Azure idle-timeout problem.
_Source: gh:mollie/mollie-api-python#339 (Mollie)_