There can be many reasons for experiencing 502 errors, but if you run into a 502 when making a call to Freshservice PATCH /incidents/{id} and not when making other GET calls the issue is likely in your payload. In Freshservice all fields are permitted for update except: 

• description 
• description_html

Therefore, be sure to exclude these fields from the request body when you perform PATCH calls to this endpoint. If you attempt to PATCH /incidents/{id} with an updated description value, a 502 will be returned with a provider message containing a very lengthy HTML body that does not explain the cause for the error and culminates in this message:

We're sorry, but something went wrong.
We've been notified about this issue and we'll take a look at it shortly.