You need to execute a query to get all the Work item for a particular Iteration path. After executing a query, get the work items using the IDs that are returned in the query results response. You can get up to 200 work items at a time. Please refer to this article:
The sample is as below:
"query": "Select [System.Id], [System.Title], [System.State] From WorkItems Where [System.IterationPath] under 'MRI_SCRUM_GIT'"