The HTTP method used in the token request is hard coded to POST and there seems to be no way of changing that. The current API I am working with only works with PUT requests (https://developers.pinterest.com/docs/redoc/combined_reporting/#section/User-Authorization/Exchange-the-code-for-an-access-token). If some OAuth standard requires this specific method, let me know and I will report the bug to the API maintainer. Thanks in advance!