error on GET request

let

  // POST request to fetch login key

    url = "https://bam.htasoftware.eu/pcuitvaart/api/apilogin",

    body = "{ ""Username"": ""XXXXXXX"", ""Password"": ""XXXXXXXXX""}",

    Parsed_Json = Json.Document(body),

    BuildQueryString = Uri.BuildQueryString(Parsed_Json),

    token = Json.Document(Web.Contents(url,[Headers = [#"Content-Type"="application/x-www-form-urlencoded;charset=UTF-8"], Content = Text.ToBinary(BuildQueryString) ] )),

    bearer = "bearer ",

    key = bearer & token,

    // GET request to fetch data

    adress = "https://bam.htasoftware.eu/pcuitvaart/api/queryapi/getqueryresult"

in

  Web.Contents(adress,[Query=[ #"query" = "Test"], Headers=[ #"Authorization" = key]])

In Power Query I wrote a script to send a POST request to fetch a key and a GET request to fetch data.
If I return the key, copy and paste it in an online API tester, everything works fine. However if I run the query I get an error:

(500): Internal Server Error

Any suggestions?