Cannot register external users using billManagementUsers REST API

Hello,

We're trying to run above payload, but where receiving this error: "You must create dchai_esmb-dev15@oraclepdemos.com in Human Capital Management to register the user in Bill Management. (ARB-5115058)

POST: https://fa-ccc-saasfademo1.ds-fa.oraclepdemos.com/fscmRestApi/resources/11.13.18.05/billManagementUsers

{"Name": "Dong Chai",

"EmailAddress": "dchai_ccc@oraclepdemos.com",

"AccountNumber": "59300",

"CustomerName": "Dixon Industries"}

As per attached document, we are able to Register External Users Using Oracle Application UI, but not using REST

API.https://docs.oracle.com/en/cloud/saas/financials/25b/faofc/register-external-users.html

Could you kindly help or advice with this issue?

Thank you,

Raluca