discover payment network is not working with PLN currency code

I am facing one issue with Apple Pay payment when using discover card for Poland country site. For Poland country we are using currency Code as "PLN". During apple session creation also we are sending "PLN" currency code only.

Our financial institution is Adyen. When doing apple pay payment using discover card with "PLN" currency code, authorization is failing. If we select any other card visa or amex it is working fine. On contacting our financial institution they confirm that in the payment blob received from Apple the expected currency is "USD" but we are sending it as "PLN". So Adyen is throwing validation error.

So please let us know why "USD" is send in payment blob even though we are initializing the session with "PLN" currency code? If Apple do not support "PLN" currency code for discover card please do mention what all currencies are supported for discover card.

Thanks & Regards,

Fatik