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Custom Connector : Flow subscription to my API fails.

We have an API developed in ASP.NET MVC Web API. We recently made it WebHook enabled using Microsoft's own ASP.NET WebHook ( So now my API exposes few events using WebHook.


Now I have created custom connector for Microsoft FLOW which is using triggers from my API. I have created custom connector successfully. Now when I am creating a FLOW using one of event from custome connector, FLOW triggers subscription request to my API. All good so far. But Subscription request getting failed because callback url provided by FLOW is not reachable as per exception from ASP.NET webhook. When i looked into code of ASP.NET webhook, what i found is it is trying to validate the URI by making HTTP GET request on callback URL with query string parameter echo and expecting to get same value back. But FLOW callback URL doesnt support HTTP GET request. And hence trigger subscription is failing. The way validation logic is written, if we are passing noecho as one of querystring paramter, it wont trigger this request. But I havent found way to instruct FLOW to pass noecho param in callback URI.


Has anyone face any such issue? Or created custom connector with FLOW with talks to ASP.NET WebHook implementation? 

Community Support
Community Support

Hi @pbijvani,


Can you please share your swagger file so that I will involve other guys to look into this?




Community Support Team _ Mona Li
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

You can look at my swagger file at below location.




Not applicable

Hi @pbijvani , how did you determined notificationURL for your custom connector?

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