Azure DevOps + Deployment Pipeline Integration Error

Just a follow-up for anyone who comes across this in the future - we were able to use Kevin's solution, except instead of authenticating in a separate PowerShell step in the pipeline, we added this into the DeploymentPipelines-DeployAll script. We had to pass additional parameters into the script, but the only one not mentioned in Kevin's solution was the Subscription ID. This is the updated SetFabricHeaders function:

function SetFabricHeaders() {
    # Login to Azure
    #Connect-AzAccount | Out-Null
    $SecureStringPwd = ConvertTo-SecureString $SPNSecret -AsPlainText -Force
    $pscredential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $servicePrincipalId, $SecureStringPwd
 
    Connect-AzAccount -ServicePrincipal -Credential $pscredential -Tenant $tenantId -Subscription $subscriptionId
 
    # Get authentication
    $fabricToken = Get-AzAccessToken -ResourceUrl $global:resourceUrl
    $plainToken = [Runtime.InteropServices.Marshal]::PtrToStringAuto(
        [Runtime.InteropServices.Marshal]::SecureStringToBSTR($fabricToken.Token)
    )

    $global:fabricHeaders = @{
        'Content-Type' = "application/json"
        'Authorization' = "Bearer $plainToken"
    }
}

I used what was in your script, the variables are passed via variable groups in the library as you recommended: