Unable to create any JSM Change requests – ProForma endpoint returns HTTP 400 Invalid request payloa

We are currently unable to submit any Change request types in our Jira Service Management Cloud project.

When attempting to submit a Change request, the user receives:

“We couldn't create your work item. Please try again later.”

This is affecting all of our Change request forms, rather than one specific request type/form.

We investigated the failed request using browser Developer Tools and found that JSM is making the following request:

POST /rest/proforma/internal/1/issue

The request returns:

HTTP 400 Bad Request

Response:

{"errorMessages":["Invalid request payload. Refer to the REST API documentation and try again."]}

The submitted payload contains the expected project, issue type, request type and ProForma/JSM Form information. One example includes:

issueType.id: 10006

requestTypeId: 228

The request also contains a form object with fieldAnswers and a valid templateFormId.

We have confirmed that Jira Service Management currently reports operational status. We also observed that Jira's status page has shown differing status for the Create and edit component, so we'd like Atlassian to confirm whether there is a known platform-side issue that could cause JSM Forms/ProForma issue creation requests to return this HTTP 400 response.