Power Query- M Language - Failure to Request a json service API -

Hi, people. I really need a helping hand, since i've been trying to solve this problem for one week, but it seems to be impossible to get it alone. The question is: this "M" code (below) makes a https url request to another endpoint for a second time (urlRequest = "https://api-sandbox.anbima.com.br/feed/precos-indices/v1/titulos-publicos/mercado-secundario-TPF") . It runs fine until the step which the M script receives the access_token: the authentication process is running well so far. Unfortunatelly, after this previous step, when i call a JSON service for the second time, the Power Query shows a box with the following message: "Specify how to connect". When I click the box buttom, Power Query shows me a window to choose the authentication method to allow the conection. Then, I select the "anonymous" option. After that, Power BI shows me, again,  another message box; "it's not possible to authenticate with the credencials".  My knowledgment about this environment stops here... The problem seems to be at the urlRequest object in the script, but I don't know how to fix it. Any help would be very apreciated! Thanks in advance, José. 

Here is the M code:

let
body = "{
""grant_type"" : ""client_credentials""
}",

minhaURL = "https://api.anbima.com.br/oauth/access-token",
getToken = Json.Document(Web.Contents(minhaURL,
[
Headers=[#"Content-Type"="application/json",
#"Authorization" = "Basic "&Binary.ToText(Text.ToBinary("Uw6QvcZwzRtp:qaRCeKStnXhE"), 0)
],
Content=Text.ToBinary(body)])
),

access_token = getToken[access_token],
authToken = "bearer " & access_token,

//urlRequest= path & "/feed/precos-indices/v1/titulos-publicos/curvas-juros",
urlRequest = "https://api-sandbox.anbima.com.br/feed/precos-indices/v1/titulos-publicos/mercado-secundario-TPF",
//keyPhrases = KeyPhrases(),
results = Json.Document(Web.Contents(
urlRequest,
[
Headers=[#"Content-Type"="application/json",
client_id = "Uw6QvcZwzRtp",
access_token = authToken
]
]
)
)
in results

The window below show the problem. The text is written in portuguese language.