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Error when using HTTP to create a new subsite in SharePoint Online



Relatively new to Flow & REST API logic, so apologies if this a) has already been asked, or b) if this is an elementary question!


Having successfully built in SharePoint Designer using the Call HTTP function, I'm now trying to replicate the logic of creating a new subsite, in a different site collection, when a user submits a request to an SP list.


Within my Flow I have a HTTP component, set up as follows:


Method: POST
Uri: https://<site collection address of where the subsite is to be made>/_api/web/webinfos/add

Headers: Accept & Content Type, both with the standard application/json;odata=verbose




"parameters": {

     "Url": "project1",

     "Title": "Project One",

     "Description": "A description of Project One",

     "Language": "1033",

     "WebTemplate": "STS#0",

     "UseUniquePermissions": true,

     "__metadata": {"type": "SP.WebInfoCreationInformation"}



(my body is hard coded for now to test the logic, after which I will pull the fields from the SP list to populate accordingly)


In my Advanced Options, I am using Basic Authentication & have applied the username & password of a service account that is a site collection administrator (and indeed a Global Admin acc for our O365 domain).


Running the above gives me the following error:


{"error":{"code":"-2147024891, System.UnauthorizedAccessException","message":{"lang":"en-US","value":"Access denied. You do not have permission to perform this action or access this resource."}}}


I was used to seeing this when developing this in SharePoint Designer, the well-known fix of specifying the WF Apps Permission Request in XML & trusting said App meant that exactly the same HTTP build has worked fine in SharePoint Online, having registered the workflow GUID & applied the XML logic of Scope="http://sharepoint/content/tenant" Right="FullControl".


Is there something similar I need to do for this call to be accepted from Flow to SharePoint Online, or have I missed a vital step in Flow?


Any insight, help or tips would be most appreciated.



Community Support
Community Support

Hi @CraigWhiteKCL,


I have escalated this issue to the product team and will get back once I received any update.




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.

Thanks @v-monli-msft, much appreciated & look forward to receiving a response in due course

Hi @v-monli-msft


Is there any feedback on this yet?



In my requestHeaders Dictionary, I had to add the following to get this to work:


Name: Authorization

Type: String



The value left blank


This zero's out the authorization header and it no longer complains

That seems to work fine in SharePoint Designer but not in MS Flow. I've put what you suggested in the "Headers" section of the HTTP call, but without success (have since removed this addition)



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