AAWP Plugin "The request has not been correctly signed." Looking for help!

I just unlocked Amazon's affiliate API and got AAWP.

After submitting my information after installing the plugin, it's saying "Invalid Signature"

I submitted everything properly. What could be the reason?

I checked their website and there isn't much information on this issue.

Thank you, BHW!

Same problem on one of my new site. I downloaded it off BHW, maybe that was the problem?