Power BI - Need data from a POST Api

Please follow the documentation. Use a body payload. https://learn.microsoft.com/en-us/powerquery-m/web-contents#example-2

Yes. You should try running the following two examples (check the "json" fields in the result to see if your program is correct). I believe you will truly understand how to post data.

let
    resp = Web.Contents(
        "https://httpbin.org", 
        [
            RelativePath = "post", 
            Content = Json.FromValue([A = 1, B = "2025/01/02"])
        ]
    ), 
    data = Json.Document(resp)
in
    data

let
    resp = Web.Contents(
        "https://httpbin.org", 
        [
            RelativePath = "post", 
            Content = Text.ToBinary("{""A"": 1, ""B"": ""2025/01/02""}", TextEncoding.Utf8)
        ]
    ), 
    data = Json.Document(resp)
in
    data