Having a bit of a weird issue with production mode using REST. - This error has suddenly started appearing after having had about a year of perfect operation of an online cart.

The issue is not present in sandbox and it works perfectly fine. - The issue is only in production mode, payments are going through fine, just when it is supposed to return the information about the payment to the webpage, it gives this error meaning I am unable to feedback to the website's database the information about the purchase.

Error given in the console after payment is made is this:

"Error: PERMISSION_DENIED at Object._RECEIVE_MESSAGE_TYPE.(anonymous function) [as postrobot_message_response] (https://www.paypalobjects.com/api/checkout.js:2569:31) at receiveMessage (https://www.paypalobjects.com/api/checkout.js:2614:60) at messageListener (https://www.paypalobjects.com/api/checkout.js:2635:13)"

Any help would be greatly appreciated!