I'm also facing exactly same issue, I have configured Alexa Skill Configuration for the implicit Grant, the token is being generated on our server and being sent to the redirect_url with all required parameters as explained in the alexa doc, but I'm still getting the issue 'Unable to link your skill, please try again.' Below is my redirect url format.
Any help is appreciated.
https://pitangui.amazon.com/spa/skill/account-linking-status.html?vendorId=MXXXXXXXXXX6#state=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&token=9b4444444444444444444444444f9&token_type=Bearer