Change notice - Update in simultaneous transitions of an issue via API

The Jira Cloud API does not support simultaneous issue transitions on an issue to stop incorrect or duplicate data from being saved to an issue. Currently, if multiple issue transitions are requested at the same time, only one of those transitions will succeed, and the rest of those requests will return a 400 error code.

In the case described above, where transitions requested via the Transition Issue API (POST /rest/api/3/issue/{issueIdOrKey}/transitions) are blocked due to an existing issue transition being executed, we will soon be replacing the 400 (Bad Request) status code with 409 (Conflict).

Why switch from 400 to 409?

The reason for witching from the 400 status code to 409 is because the latter more accurately describes the reason for the API request failing. In the case where your app receives a 409 error code, it should employ a retry mechanism.

When will this change take effect?

The change will be rolled out no sooner than May 4, 2020.