Sandbox requesttopay blocked by WAF from cloud servers — requesting IP whitelist

Hi, I'm integrating the MoMo Collections API (sandbox) into a server-side application. Requests to /collection/v1_0/requesttopay are being rejected with a WAF block page ("Request Rejected... The requested URL was rejected. Please consult with your administrator") when sent from my cloud-hosted server (Render.com), even though the exact same request succeeds when sent from my local machine using identical code and credentials. Could someone confirm whether cloud/datacenter IP ranges are blocked in sandbox, and if so, help whitelist these outbound IP ranges for my app? 74.220.51.0/24 74.220.59.0/24 Account details: API User ID: b3342b64-ffd2-4746-a771-b884953cc72e Thank you!