Example below illustrates how configure callback url in sandbox
Given callback URL is https://momocallback.mtn.com/sandbox0000 , the callback host will be momocallback.mtn.com
Configure the body of API_USer request as below as below
{
"providerCallbackHost": "momocallback.mtn.com"
}
API_USER SandBox can be generated from https://momodeveloper.mtn.com/docs/services/sandbox-provisioning-api/operations/post-v1_0-apiuser/console