Channel Advisor API Connection with auth key creation

Hi TrysHisBest 

Your username and password are passed in Authorization Header with Basic Auth type, not in Body, so they should be in Headers parameter rather than Content parameter of Web.Contents().

I did some google searching for passing basic Authorization username and password, and found a blog and a thread:

Using Power Query to get data from an API that uses a Username and Password combination

Passing username and password in Basic authentication (microsoft.com)

Both suggest to put username and password in username:pasword format, then encode the string with base64 encoding. Then put the encoded string into Headers. For encoding use the link https://www.base64encode.org/

Based on above, you could try below code

let
    url = "https://api.channeladvisor.com/oauth2/token",
    headers = [#"Authorization"="Basic xxxxxxxxxxxxx"],
    postBody = [
        grant_type = "refresh_token", 
        refresh_token = "xxxxxxxxxxxxxxxx"
        ],
    response = Json.Document(Web.Contents(url,
        [
            Headers = headers,
            Content = Text.ToBinary(Uri.BuildQueryString(postBody))
        ]))
in
    response

If you can get correct token by using above code, then you can transform the query to a custom function so that it can be called by other queries. Just add () => before let:

() =>
let
    url = "https://api.channeladvisor.com/oauth2/token",
    headers = [#"Authorization"="Basic xxxxxxxxxxxxx"],
    postBody = [
        grant_type = "refresh_token", 
        refresh_token = "xxxxxxxxxxxxxxxx"
        ],
    response = Json.Document(Web.Contents(url,
        [
            Headers = headers,
            Content = Text.ToBinary(Uri.BuildQueryString(postBody))
        ]))
in
    response

Then create another query for the GET request which calls the function. Assume the earlier custom function query is called GetAccessToken.

let
    Source = Json.Document(Web.Contents("https://xxxxxxxxxxxxxxxxxxxx", [Headers=[#"Authorization"="Bearer "&GetAccessToken()]]))
in
    Source

Hope this helps.

Jing