Error (404) Importing a PBIX file (from blobstorage) into a PowerBI Group

I am getting trying to upload >1gb pbix from blobstorage in A4 capacity backed workspace using PostImportInGroupAsync API call:

var inf = new Microsoft.PowerBI.Api.Models.ImportInfo()
                {
                    FileUrl = uploadUrl,                  
                };
var import = await client.Imports.PostImportInGroupAsync(new Guid("878be823-1928-474c-98d2-848ade1e4890"), "newmyreportdda", inf,ImportConflictHandlerMode.Overwrite); 

but getting Bad request:

Microsoft.Rest.HttpOperationException: 'Operation returned an invalid status code 'BadRequest''

Microsoft.Rest.HttpOperationException   HResult=0x80131500   
Message=Operation returned an invalid status code 'BadRequest' Source=Microsoft.PowerBI.Api   

StackTrace:    
at Microsoft.PowerBI.Api.ImportsOperations.<PostImportInGroupWithHttpMessagesAsync>d__25.MoveNext() 
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()    
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)    
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)    
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult() 
at Microsoft.PowerBI.Api.ImportsOperationsExtensions.<PostImportInGroupAsync>d__25.MoveNext() 
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()    
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)    
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)    
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()  
at PowerBIAuth.Program.<Main>d__5.MoveNext() 
in C:\Users\vz112ss\Downloads\PowerBIAuthNew\PowerBIAuth\PowerBIAuth\Program.cs:line 50


  This exception was originally thrown at this call stack:
    [External Code]
    PowerBIAuth.Program.Main(string[]) in Program.cs