Receiving http 401 error on API call after generating, refreshing access token

I'm using the Oauth2 Authorization Code flow.  I have obtained an access token and refresh token and am now trying to GET All Contact Lists. I continue to receive http status code 401, immediately after refreshing the token successfully.

I tried adding a new account, removing browser cookies, re-confirmed the access, generated new tokens and still receive the 401 error when issuing an API Get/Post immediately after the token access is granted and refreshed.

I am out of ideas at this point.  

Sample Access Token Response:

{

            "token_type": "Bearer",

            "expires_in": 86400,

            "access_token": [removed],

            "scope": "account_read offline_access account_update campaign_data contact_data",

            "refresh_token": [removed]

}

Sample GET URL:

https://api.cc.email/v3/contact_lists?include_count=true&include_membership_count=all

Bearer value Submitted:

[removed]

Sample GET Response:

{

            "error_key": "unauthorized",

            "error_message": "Unauthorized"

}