ERROR: The order currency (USD) does not match the customer currency (), and currency override is not allowed in the customer settings.

@madhu  I think you did not enable it in the right customer record. Go to the external system(bigcommerce) and try to find the Customer for that concerned order. Get the external reference number of that customer and then try to filter the customer records with that reference number in the Sync History(BC301000) form. Once the right customer is found, then you can enable this checkbox. Also, you can enable this in the Customer Classes(AR201000) for the customer class which you are using for your store so that it applies for future new customers. 

@madhu ,

I’ve seen the same issue, and enabling the override didn’t help. What fixed the issue for me, was to set the customer currency to USD (a field on the customer record, to the left of the Enable Currency Override. Try that and let us all know if that helps.

I agree with @KarthikGajendran , that you have to be 100% sure you’re modifying the right customer.

Good luck!

@praveenpo 

I enable that future but it  not working