PayPal Error: Security header is not valid. Please check your API Credentials and try again. Also please note that Test mode is ON!

This is the error I'm getting. I've read a lot of posts from many years ago but there didn't seem to be any definitive answer and it says to make sure that you have SHA256, which I have verified, it also says Verisign G5 certificate, which Paypal informs me was decommissioned in April this year, so I'm wondering if the Paypal Pro is out of date on this certificate. Also I'm in Canada and thinking that maybe the extension is requesting API calls from the US server and not the Canadian. I noticed in one PHP script from the extension it indicates paypal.com/us/...

I ran a test HTML script from a paypal forum and it works just fine.

Any suggestions?

I really like this cart and would like to make this work.

Paypal Standard gives me a process error that something is wrong ... and I get the same error as above for Paypal express.