Marketplace Error Signature Hash Does Not Match

I'm trying to set up the connection to the marketplace. I have an OpenCart account and my store is set up. I am copying the API secret Key from there and pasting it into the window on my backend. I click the button, it takes a moment and the little red [!] triangle is there with an error when I hover on it:

"Signature Hash Does Not Match!"

What might be the problem?

Following