What does HMAC calculation for HPP: Signature not valid mean?

Merchant signature was not valid

The error Merchant signature was not valid means your HMAC signature isn’t calculated correctly. The error is shown on Hosted Payment Pages (HPP) when the HMAC signature you’re sending us isn’t corresponding with the HMAC signature we calculated.

Tip: Learn how to implement HMAC signature calculation.

Note: The Hosted Payment Pages (HPP) integration is being deprecated. Find out more about the time-line and necessary actions here.