Users receive the aforementioned response when making API calls.
The upstream server may have returned an empty response or cut the response off early so it was unable to complete the proxying process. A proxy error means actual connectivity issues between Tyk and the target host (i.e., a connection-level issue with the downstream server misbehaving for some reason).
Expired TLS certificates may also cause issues.
Users are advised to upgrade to the latest versions of any Tyk packages at their earliest convenience as a patch was released to resolve this issue. Packages are available to download from Packagecloud.io Further details on how to upgrade can be found in our docs. It may also be worth checking if any TLS certificates associated with the domain have expired.