Hello,
This is unfortunately a limitation of our API today where a customer is "locked" into a currency for subscription after the first one is created. If your Customer had a Subscription in USD, then they can only get new Subscriptions in USD in the future. Attempting any other currency will error as you experienced. If you want to change the currency, you will have to create a brand new Customer object and collect payment method details again.
It's something we want to fix in the future but it won't be soon. We've recently fixed this limitation for one-off Invoices but it was quite complex and it will take longer for Subscriptions to work around that limitation.
Hope this clarifies the issue.
Best,
Remi