Unable to rename subsite URL via CSOM in SharePoint Online - sharepoint

Question

I have set up a SharePoint Online site and I have created a provider hosted app. One of the features of the app is to create subsites and there are times when a subsite needs to be renamed, including renaming the subsite URL. I can use the CSOM to create the subsite without any problems but when I try to rename the URL I get an access denied error. If I only change the title and description of the subsite there is no problem. If I log into SharePoint Online via the browser (using the same user account!) and I use the UI to rename the URL then it works without any problem. The page in SharePoint I use to rename the URL is https://tenant.sharepoint.com/testproject/_layouts/15/prjsetng.aspx
I have tried this on both a Microsoft 365 Developer subscription (where I am doing most of my development and testing) and the main SharePoint Online site where the solution will eventually be deployed to. I don't know much of the details for the main SPO site, other people set it up and I was provided an account to test renaming the subsite. To be clear, I am able to rename the subsite URL via the UI in both the developer and main SharePoint Online sites.
Is there something I'm doing wrong? Is there a limitation to renaming a subsite URL via code in SharePoint Online? Is there a bug in SharePoint Online that prevents renaming a subsite URL using code?
The exception thrown includes ServerErrorTypeName = "Microsoft.SharePoint.SPException". I can get the correlation id but from what I understand that's of no use in SharePoint Online. The exception Message is literally "Access denied." There is no inner exception.
Here is the code I'm using to rename the subsite:
SharePointContext spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext);
ClientContext clientContext = new ClientContext(spContext.SPHostUrl)
{
Credentials = new SharePointOnlineCredentials("SPUserName", "SPPassword".ToSecureString())
};
var webUrl = request.OldProjectUrl;
var subweb = clientContext.Site.OpenWeb(webUrl);
clientContext.Load(subweb);
clientContext.ExecuteQuery();
subweb.Title = request.ProjectName;
subweb.Description = request.ProjectName;
subweb.ServerRelativeUrl = "/HardcodedForTesting"; // <-- if I skip this line there is no error
subweb.Update();
clientContext.ExecuteQuery();

Answer 1

I was trying to achieve the same result but encountered the same error.
I was able to solve this by disabling the NoScriptSite setting of the site collection.
Using the PnP.PowerShell module:
Set-PnPSite -NoScriptSite:$false
Also the value you give to the ServerRelativeUrl property must be correctly constructed. I found two allowed format:
/sites/site-collection-path/new-subsite-path
new-subsite-path

Answer 2

Just did a test on my environment, I could rename the subsite URL via CSOM code normally. I use the same code as yours.
For your issue, you'd better create a service request with Microsoft.