Adding a template to multiple existing sharepoint sites

Question

I have made a code for adding a template to multiple existing SharePoint sites at once with foreach and Import-csv. I think it almost works but I keep getting the same error.

PS C:\WINDOWS\System32> $adminUrl = "https://lk6y-admin.sharepoint.com"
>> Connect-SPOService -Url $adminUrl
>> $templateName = "STS#0"
>> $existingSites = Import-Csv -Path "C:\Users\stijn.mensink\try.csv"
>> $site = $site.SiteUrl
>> foreach ($site in $existingSites) {
>>     $siteUrl = $site.SiteUrl
>>     $siteRelativeUrl = $site.SiteRelativeUrl
>>
>>     try {
>>         # Get the existing site
>>         $existingSite = Get-SPOSite -Identity $siteUrl -Detailed
>>
>>         # Add the site template to the existing site
>>         $web = Get-SPOWeb -Identity $existingSite.Url
>>         $web.ApplyWebTemplate($templateName)
>>         $web.Update()
>>
>>         Write-Host "Template '$templateName' added successfully to $siteUrl ($siteRelativeUrl)" -ForegroundColor Green
>>     }
>>     catch {
>>         Write-Host "Failed to add the template to $siteUrl ($siteRelativeUrl). Error: $($_.Exception.Message)" -ForegroundColor Red
>>     }
>> }

I keep getting the same error:

Failed to add the template to (). Error: Cannot bind argument to parameter 'Identity' because it is null. I have checked the csv multiple times. I don't understand why it doesn't recognize the value

I was expecting that the code would pick up the value of the $siteUrl that is in my csv