InvalidRequestError: Either of payment method details or tmp token input should be specified. - Bancontact
This error is seen when you create the permanent token by payment method as "card" or "Bancontact" and pass Bancontact as the payment method.
Bancontact is a one-time payment method, so there won’t be any permanent tokens available, but if you want to use permanent tokens make sure you use the Sepa payment methods as permanent tokens.
Related Articles and Documentation
Configure Adyen Bancontact in Chargebee