Assign a document to a checklist item. The document must already exist on this listing (upload via POST /api/files/listings/{listingGuid}/documents). The checklistItemId must be the ActivityId from the checklist array returned by GET /api/files/listings/{listingGuid}. Fetch the listing, identify the target checklist activityId, then call this endpoint with the document GUID.

Validation & Requirements

Required Parameters

• listingGuid (path, string, format=guid)
• checklistItemId (path, integer, format=int32)
• form (body, object)

Required JSON Body Fields

• documentGuid (format=guid, minLength=1)

Validations

• Invalid GUID values in *Guid/*Guids fields return 422 Unprocessable Entity.
• Invalid date values in *date* fields return 422 Unprocessable Entity.
• Missing required request body returns 422 Unprocessable Entity with Missing request body..
• Additional business-rule validation may return 422 with details in the errors array.

Integration Requirement

• Retrieve the corresponding ...Form endpoint immediately before write operations to get current dynamic required fields and allowed values.