Keep getting a 400 Bad Request error when trying to update refresh schedule via API

Hello folks,

I am developing Power BI reports and managing them via API calls as a part of my job. I have developed a number of powershell scripts to streamline management via the rest API. It all works pretty well, except when I attempt to update a refresh schedule of a report. Some details:

• Enabling scheduled refresh is done separately and is not a problem
• I have taken over or is aleady the dataset owner.
• Updating the refresh schedule consistently returns a 400 Bad Request error.

Here are the PS functions:

function EnableDatasetRefreshSchedule
{
    [CmdLetBinding()]
    param 
    ( 
        [Parameter(Mandatory=$true, Position=0)] [string] $groupId, 
        [Parameter(Mandatory=$true, Position=1)] [string] $datasetId, 
        [Parameter(Mandatory=$true, Position=2)] [string] $refreshScheduleState 
    )

    $urlRefreshScedule = "https://api.powerbi.com/v1.0/myorg/groups/$groupId/datasets/$datasetId/refreshSchedule"

    $body = '{ "value": {"enabled": '+$refreshScheduleState+' }}'

    Invoke-PowerBIRestMethod -Url $urlRefreshScedule -Body $body -Method PATCH
}

function UpdateDatasetRefreshScheduleTime
{
    [CmdLetBinding()]
    param 
    ( 
        [Parameter(Mandatory=$true, Position=0)] [string] $groupId, 
        [Parameter(Mandatory=$true, Position=1)] [string] $datasetId, 
        [Parameter(Mandatory=$true, Position=2)] [string] $refreshScheduleDays, 
        [Parameter(Mandatory=$true, Position=3)] [string[]] $refreshHours, 
        [Parameter(Mandatory=$true, Position=4)] [string[]] $refresMinutes 
    )

    $randomHour = $refreshHours | Get-Random
    $randomMinute = $refresMinutes | Get-Random

    $refreshScheduleTime = '"'+$randomHour+':'+$randomMinute+'"'

    $urlRefreshScedule = "https://api.powerbi.com/v1.0/myorg/groups/$groupId/datasets/$datasetId/refreshSchedule"

    #$body = '{ "value": {"days": ['+$refreshScheduleDays+'], "times": ['+$refreshScheduleTime+'],"localTimeZoneId": "UTC"}}'
    $body = '{"value": {"days": ['+$refreshScheduleDays+'], "times": ['+$refreshScheduleTime+']}}'

    Invoke-PowerBIRestMethod -Url $urlRefreshScedule -Body $body -Method PATCH
}

Any hints on what  might be wrong is very appreciated!

Cheers, Mike