BindToGateway Powershell REST API POST failing - Need Help

Hi,

I am struggling to get the BindToGateway REST API call to work in powershell https://docs.microsoft.com/en-us/rest/api/power-bi/datasets/bindtogatewayingroup

Below is my code for doing the API call

Invoke-PowerBiRestMethod -Url "groups/$($workspaceid)/datasets/$($datasetid)/Default.BindToGateway" -Method POST -Body $jsonPostBody

The workspace and dataset varibales are correct, and the Body is in the format:

{
"datasourceObjectIds": [
"dc2f2dac-e5e2-4v37-af76-2a0bc10f1bs5",
"3bfe5d33-ag7d-4d24-b0b5-e2b96eb01cf5"
] ,
"gatewayObjectId": "1f85e798-5852-4fdd-ab01-33cc14b6e934"
}

When I run this as a user who is an administrator on the gateway I get the error

Response status code does not indicate success: 404 (Not Found).

StackTrace : at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
at Microsoft.PowerBI.Commands.Profile.InvokePowerBIRestMethod.<INVOKERESTMETHOD>d__31.MoveNext()
Exception : System.Net.Http.HttpRequestException
InvocationInfo : {Invoke-PowerBIRestMethod}
Line : Invoke-PowerBiRestMethod -Url $url -Method POST -Body $jsonPostBody
Position : At line:1 char:1
+ Invoke-PowerBiRestMethod -Url $url -Method POST -Body $jsonPostBody
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When I run it as a service principal with all deletgated API permissions and an admin on the workspace and dataset owner I get the following error

Message: Response status code does not indicate success: 400 (Bad Request).

StackTrace : at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
at Microsoft.PowerBI.Commands.Profile.InvokePowerBIRestMethod.<INVOKERESTMETHOD>d__31.MoveNext()
Exception : System.Net.Http.HttpRequestException
InvocationInfo : {Invoke-PowerBIRestMethod}
Line : Invoke-PowerBiRestMethod -Url $url -Method POST -Body $jsonPostBody
Position : At line:1 char:1
+ Invoke-PowerBiRestMethod -Url $url -Method POST -Body $jsonPostBody
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So one gives me a 400 and the other a 404 error with no further usfull info which I can see.

Can anyone offer any suggestions? 

Thanks
Dominic