“When a Teams webhook request is received” not working from C# HttpClient

I was recently trying to send a message from my application (an Azure Function) to a Teams channel.

The current recommended way (by Microsoft) to do this is via a “Teams Workflow”, which is layer over top of Microsoft Power Automate, which is a layer over Logic apps.

Here’s my Teams Workflow:

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Here’s the same Teams Workflow in Power Automate:

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Here’s a slightly different one, which I wrote as an Azure Logic App. Here the first step is “When a HTTP request is received”:

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In both cases, I was able to trigger the Power Automate / Logic app fine from Postman, but when I tried from C# code using HttpClient.PostJsonAsync it failed.

The only difference I could see between the Postman request and the HttpClient request was that HttpClient was sending a transfer-encoding=chunked header.

I re-wrote my code to use PostAsync instead, and then it worked fine.

using HttpClient client = new();
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

var card = AdaptiveCard.ExceptionCard("parcel.changed.v1", "I800100081376", "dev", new InvalidOperationException());

var url = "https://prod-31.australiasoutheast.logic.azure.com:443/workflows/dda945b5337d48....";

// await client.PostAsJsonAsync(url, card); // this sends a transfer-encoding=chunked header, which Power Automate & Logic Apps doesn't handle

var json = JsonSerializer.Serialize(card);
var content = new StringContent(json, System.Text.Encoding.UTF8, "application/json");
await client.PostAsync(url, content);