[Auth] The authorization grant type is not supported by the authorization server

[twanlee]

Hello you guys, i'm recenly got Error getting LWA Access Token while using SDK to connect to SP API. Then i test it on Postman like instruction here: https://github.com/amzn/selling-partner-api-docs/blob/main/guides/developer-guide/SellingPartnerApiDeveloperGuide.md#step-1-request-a-login-with-amazon-access-token then i've got response: { "error_description": "The authorization grant type is not supported by the authorization server", "error": "unsupported_grant_type" }, I read a document again and again, try with LWA Credentials in my app. Seems like nothing wrong. If anyone has got this issued, please share your experience!!!!

[wyrd-code]

I also got this error at first,

while using node-fetch, and following the instructions for getting an access token via manual request from the docs.

But it turns out the issue was the HTTP request was not created properly, ie I was not using FormData to build the request body. The same values sent via Postman (Insomnia rather) worked fine, so that was a hint that I forgot something. :)

Double check how you are sending the http request and what is being sent.