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Power Automate Desktop - Invoke Web Service - 401

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Posted on by CP-30100451-0

Hi everyone,

I’m facing a 401 Unauthorized error when using the “Invoke Web Service” action in Power Automate Desktop.

Here’s my setup:

Server: Microsoft-IIS
Method: GET
Authentication: None
Tested in Postman: ✅ Works fine
In PAD: ❌ Fails with “401 Unauthorized”

Things I’ve tried:

Since this End point URL doesn't have any authentication mechanism/ headers/ Request Body. The same End Point works perfectly fine on UiPath and Postman and even there, it has no authentication mechanism but it fails in PAD.

Still getting 401.

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Expiscornovus 32,892 Most Valuable Professional on at

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Power Automate Desktop - Invoke Web Service - 401

Hi @CP-30100451-0,

Can you share a bit more details about your Postman test? Would be useful to double check that setup and compare it with the PAD action.

Additionally, I assume Postman and PAD are running on the same machine/virtual machine?

Happy to help out 😁

I share more #PowerAutomate and #SharePointOnline content on my Blog, LinkedIn, Bluesky profile or Youtube Channel

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

Hi,

Thanks for your reply, unfortunately, i cannot share the postman details here.

This is the Web response which i get from PAD, which i am not able to understand why this only for PAD and not for other tool, this doesnot have any authentication mechanism

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

Can i have an update on this please, let me know if you need more answers from me.

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Expiscornovus 32,892 Most Valuable Professional on at

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Power Automate Desktop - Invoke Web Service - 401

Hi @CP-30100451-0,

Would be useful to know if the both PAD and Postman run on the same machine? Do you have any details about that?

Additionally, can you share the setup (including the advanced settings) of your Invoke Web Service action?

Just tested an anonymous API (a Mock server with a simple Mock get request). That works fine with that action.

https://learning.postman.com/docs/design-apis/mock-apis/tutorials/mock-with-examples/

If it helps, below are my details of this test.

1. This was my test run

2. Advanced settings

Happy to help out 😁

I share more #PowerAutomate and #SharePointOnline content on my Blog, LinkedIn, Bluesky profile or Youtube Channel

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

Thanks for replying,

Both my Postman and PAD run inside the Citrix environment and on the same server.
In turn the URL works perfectly fine on UiPath and on the browser, this gives me the status code 200 and could see the JSON response on it.
Spoke to URL owner and they said they have whitelisted my authentication for the URL, since this URL doesnot have authentication mechanism, it should fail on UiPath as well, that’s the part I am not able to bypass it.

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Expiscornovus 32,892 Most Valuable Professional on at

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Power Automate Desktop - Invoke Web Service - 401

Hi @CP-30100451-0,

Just to rule out some things.

Have you tried a different API, for example a Mock API like I used in my setup and tested the setup with a different API/url on your PAD instance in Citrix?

https://learning.postman.com/docs/design-apis/mock-apis/tutorials/mock-with-examples/

Happy to help out 😁

I share more #PowerAutomate and #SharePointOnline content on my Blog, LinkedIn, Bluesky profile or Youtube Channel

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

I get 502 Bad Gateway Error, not sure this might be blocked by the org.

Tested the free API inside the server which i took it from google, seems i can get the response from PAD

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

Just checking, does PAD Supports NTLM?

If Yes, then the windows credentials passed to the Endpoint URL wont work

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Expiscornovus 32,892 Most Valuable Professional on at

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Power Automate Desktop - Invoke Web Service - 401

Hi @CP-30100451-0,

So it does have authentication, now the issue makes more sense :)

NTLM is current not supported in that action, it is listed as a known issue:

https://learn.microsoft.com/en-us/power-automate/desktop-flows/actions-reference/web#known-issues

Happy to help out 😁

I share more #PowerAutomate and #SharePointOnline content on my Blog, LinkedIn, Bluesky profile or Youtube Channel

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CP-30100451-0 14 on at

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Power Automate Desktop - Invoke Web Service - 401

Hi @Expiscornovus,

Thanks for replying, whats the alternate option to proceed further?

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