update-refresh-schedule-in-group error 415 Unsupported media type using powershell

https://github.com/mschoombee/Blog/blob/main/2020/automating-power-bi-deployments/Reports%20-%20Update%20Refresh%20Schedule.ps1 
on this github site I found the solution. 

# https://learn.microsoft.com/en-us/rest/api/power-bi/datasets/update-refresh-schedule-in-group

## once in a lifetime you got to do this: 
## Install-Module -Name MicrosoftPowerBIMgmt
## somtimes in a lifetime you got to do this:
## Update-Module -Name MicrosoftPowerBIMgmt
## Depending on your execution policy do not forget to trust the session
## Set-ExecutionPolicy -ExecutionPolicy remotesigned -Scope Process

## login to the platform
Login-PowerBI

##Build the body
 $ApiRequestBody = @"
        {
            "value": {
                "days": [
                    "Sunday",
                    "Monday",
                    "Tuesday",
                    "Wednesday",
                    "Thursday",
                    "Friday",
                    "Saturday"
                ],
                "times": [
                    "08:00",
                    "08:30"
                ],
                "notifyOption": "MailOnFailure", 
                "localTimeZoneId": "UTC", 
                "enabled": true
            }
        }
"@ 

## Invoke the API but do not include the header
Invoke-PowerBIRestMethod -Url 'https://api.powerbi.com/v1.0/myorg/groups/74601087-ad5e-481c-a20c-1965baa8607b/datasets/d469f67e-4568-49eb-b6bc-e42f2c5d37d5/refreshSchedule' -Method Patch -Body ("$ApiRequestBody")

I tried to schedule between full and half hours but then the response is 
Invoke-PowerBIRestMethod : Encountered errors when invoking the command: {
"code": "InvalidRequest",
"message": "Refresh schedule time must be full or half hour (HH:00 or HH:30)" so if you can live with that this is the solution