Invalid credentials provided error message in checkout

Hi,
I am having trouble with the plugin. While checkout with test card it says invalid credentials provided but in the woocommerce dashboard backend it says

Trust Payments payment unsuccessful, transaction id:

The security code entered was not sent to the bank.

and so on.

The log file says lot’s of things. I can’t post the log here.

22-11-2020 08:57:06 UTC - INFO - A89acegqx - Finished HTTP request to https://webservices.securetrading.net/json/.
22-11-2020 08:57:06 UTC - ALERT - A89acegqx - Exception of type Securetrading\Stpp\JsonInterface\HttpException caught with code 3 in /wp-content/plugins/secure-trading-gateway-for-woocommerce/vendor/securetrading/stpp_json/src/Http.php on line 50: "HTTP code 401.".
22-11-2020 08:57:06 UTC - ALERT - A89acegqx - Securetrading\Stpp\JsonInterface\HttpException: HTTP code 401. in /wp-content/plugins/secure-trading-gateway-for-woocommerce/vendor/securetrading/stpp_json/src/Http.php:50

The demo product that I try to purchase link is:

https://www.theflowershops.co.uk/dev/flower/solent/

How to solve this problem?

If you need access to staging site let me know.

Thanks
Shahi

The page I need help with: [log in to see the link]