Authentication failed. API credentials incorrect.

-- HikaShop version -- : HikaShop Business: 2.3.0
-- Joomla version -- : 3.2.3
-- PHP version -- : 5.3.28
-- Browser(s) name and version -- : XXXXX x.x.x
-- Error-message(debug-mod must be tuned on) -- : Authentication failed. API credentials incorrect.

When a user tries to buy something, at the point of checkout, they are receiving this error:

Authentication failed. API credentials incorrect.

Beneath that error is a bunch of code.

We haven't been in sandbox for a while now, but when we were testing it was fine. The dummy accounts would process the transaction without a problem and we would only briefly see that string of code when processing a paypal transaction. Now when it's live, the transaction freezes during checkout, exposing all that code. We get the "Authentication failed. API credentials incorrect." error. No actual payment is made, yet the buyer receives "A new order has been created on your website" email, the seller and administrators (us) recieve similar messages, giving everyone the very untrue idea that a transaction was made.

Can you please help us with this? Thank you.

Kind Regards,
OurBlok

PS I updated the Hikashop (market) Paypal Adaptive Payment Plugin because the app-id that was there was the sandbox id, but we are still receiving the same error. Thanks in advance!

All the credentials seem to be fine.

Thanks for your help!