I am on the quickbooks-ruby oauth2 branch and everything worked until today. Now every POST to create a customer or invoice fails with a weird XML error that just shows [placeholder] as the error message. Nothing in my code changed. Sandbox and production both fail. Any idea what happened?

Intuit changed their responses to be gzip-compressed without telling anyone, and the gem's Faraday connection did not always have the gzip middleware registered, so the raw compressed response was parsed as XML and blew up with the cryptic [placeholder] error. The fix was in the gem: always rebuild the Faraday connection with gzip support. Update quickbooks-ruby to a version that includes the gzip fix on the oauth2 branch. If you are pinned to an older commit and cannot update, the workaround is to register gzip explicitly when building the OAuth2 client: pass a block to OAuth2::Client.new that does builder.use :gzip, builder.request :url_encoded, and sets the adapter.

Source: https://github.com/ruckus/quickbooks-ruby/issues/421