Getting 403 error on Payment Authorization API call

ahsanaa00 — Mon, 13 Apr 2026 05:27:06 GMT

Hi everyone,

I'm integrating Cybersource REST API for payment authorization and keep getting a 403 Forbidden error on every request. I've double-checked my credentials but can't figure out what's wrong.

My Setup:

Environment: Sandbox
API: REST (not SOAP)
Language: PHP 8.1
SDK: Official Cybersource PHP SDK (latest version)

Error Response:

{  "status": "FORBIDDEN",  "reason": "INVALID_MERCHANT",  "message": "Access denied"}

What I've tried:

Regenerated API keys from Business Center
Verified Merchant ID is correct
Confirmed HTTP Signature headers are properly formatted
Tested with Postman — same error

Is this a sandbox account activation issue or am I missing something in the authentication setup? Any help would be appreciated.

Thanks

topic Getting 403 error on Payment Authorization API call in cybersource APIs

Getting 403 error on Payment Authorization API call