PayPal has a sandbox development environment to test project requirement flows, but instructions found in the documentation and forums are consistently vague and at times categorically incorrect. If troubleshooting documentation leads to cycles around the same pages, it’s a problem. For instance, this message I received when attempting to process a GetRecurringPaymentsProfileDetails request:

PayPal error code: 11546 “Profile ID is not valid for this account. Please resubmit request with the correct profile ID.”

The API error codes indicate this error number is “Merchant account is denied” (with no resolution in sight.) There wasn’t a single Google result for the former error message or a useful match for the latter. Not to mention nada in the now-defunct forums. The problem? The PayPal profile I was attempting to access was created with another API key that I had since changed. It is an easy-to-describe error obscured by poor feedback that can happen innocuously when switching between environments in dev mode.

So in summary:

You likely changed your API key on but haven’t updated your project to use that key.