New API Endpoint with DAX Queries

I have exactly the same kind of issue as you rjhale. Same error message.
I have also verified that the Rest API is enabled in the admin portal and that I have build access to the dataset.

$requestUrl = 'https://api.powerbi.com/v1.0/myorg/datasets/e500cd5d-4e48-4feb-80d5-33435a5c9a16/executeQueries'

$requestBody = @"
{ “queries”: [{“query”:”EVALUATE SUMMARIZECOLUMNS('Movements[countryCode]', \"Ship Count\", [shipCount])“}], “serializerSettings”:{“incudeNulls”: true}}
"@

Write-Host $requestBody

Write-Host 'Logging in'
Login-PowerBI
Write-Host 'Logged In'
$result = Invoke-PowerBIRestMethod -Method POST -Url $requestUrl -Body $requestBody
Resolve-PowerBIError -Last
Write-Host 'Invoked'
$result
$parsed = $result | ConvertFrom-Json
$parsed.results[0].tables[0].rows | Format-List
Write-Host 'Done'

I get the following response:

Logged In
Invoke-PowerBIRestMethod : One or more errors occurred.
At C:\Users\lchh\OneDrive - Bunker Holding Group\PowerShell\SampleDaxRestAPI.ps1:26 char:11
+ $result = Invoke-PowerBIRestMethod -Method POST -Url $requestUrl -Bod ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : WriteError: (Microsoft.Power...werBIRestMethod:InvokePowerBIRestMethod) [Invoke-PowerBIRestMethod], AggregateException
+ FullyQualifiedErrorId : One or more errors occurred.,Microsoft.PowerBI.Commands.Profile.InvokePowerBIRestMethod

Exception : System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
at Microsoft.PowerBI.Commands.Profile.InvokePowerBIRestMethod.<InvokeRestMethod>d__35.MoveNext()
InnerException : False
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__35.MoveNext()
HelpLink :
Source : System.Net.Http
ErrorDetails :
ErrorCategory : WriteError: (Microsoft.Power...werBIRestMethod:InvokePowerBIRestMethod) [Invoke-PowerBIRestMethod], AggregateException
InvocationInfo : System.Management.Automation.InvocationInfo
ScriptStackTrace : at <ScriptBlock>, C:\Users\lchh\OneDrive - Bunker Holding Group\PowerShell\SampleDaxRestAPI.ps1: line 26

Invoked
Cannot index into a null array.
At C:\Users\lchh\OneDrive - Bunker Holding Group\PowerShell\SampleDaxRestAPI.ps1:31 char:1
+ $parsed.results[0].tables[0].rows | Format-List
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : NullArray

Done

Anonymous is there anyway that this is not rolled out to our Power BI tenants?