alt Hacker NewsIt really depends on the third party service.
For service A, a 500 error may be common and you just need to try again, and a descriptive 400 error indicates the original request was actually handled. In these cases I'd log as a warning.
For service B, a 500 error may indicate the whole API is down, in which case I'd log a warning and not try any more requests for 5 minutes.
For service C, a 500 error may be an anomaly and treat it as hard error and log as error.
What's the difference between B and C? API being down seems like an anomaly.
Also, you can't know how frequently you'll get 500s at the time you're doing integration, so you'll have to go back after some time to revisit log severities. Which doesn't sound optimal.