Error X-CHC-MN-Attachments-Payer Field is Mandatory

When using the Medical Network Attachment Retrieval v1 API in the sandbox to send a request, the error: “X-CHC-MN-Attachments-Payer field is mandatory” shows.

Can you please confirm that the URLs that you are using https://sandbox-apigw.optum.com/apip/auth/v2/token and https://sandbox-apigw.optum.com/attachments/retrieval/v1/search. Search to retrieve a set of document IDs based on the upload date range, attachment control number, patient first name, last name, member ID, provider ID, provider first name, organization name, claim service start date, and claim service end date. By default, testMode is set to false to retrieve the production data. To retrieve the test data, pass the query string as testMode=true.