Problem in Deleting Remote Event Receiver in Sharepoint

You need to remove the remote event reciever using the same ClientID that created it. So if your provider hosted app with a specific clientid was used to create the event reciever you will get access denied if you try to delete it with powershell using your credentials. However i do believe that the pnp powershell Connect-SPOnline has some parameters to connect with clientid and secret. You should be able to delete it then

I do

You can do this first by searching it in the SharePoint ClientBrowser and then use a powershell script to delete it.

function Get-SPOListEventreceivers
{
param (
  [Parameter(Mandatory=$true,Position=1)]
		[string]$Username,
		[Parameter(Mandatory=$true,Position=2)]
		$AdminPassword,
        [Parameter(Mandatory=$true,Position=3)]
		[string]$Url,
        [Parameter(Mandatory=$true,Position=4)]
		[string]$ListTitle,
        [Parameter(Mandatory=$true,Position=5)]
		[GUID]$EventReceiverGUID
)

  $ctx=New-Object Microsoft.SharePoint.Client.ClientContext($Url)
  $ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Username, $AdminPassword)

try
{
$ctx.ExecuteQuery()
} catch [Net.WebException] 
        {
            
            Write-Host $Url " failed to connect to the site" $_.Exception.Message.ToString() -ForegroundColor Red
}

 $ctx.Load($ctx.Site)

  $lista=$ctx.Web.Lists.GetByTitle($ListTitle)
 $ctx.Load($lista)
  $ctx.ExecuteQuery()
 $recevery=$lista.EventReceivers
 $ctx.Load($recevery)
 $ctx.ExecuteQuery()
 Write-Host "Found " $recevery.Count " receivers in " $lista.Title

$recevery.GetById($EventReceiverGUID).DeleteObject()

try
{
$ctx.ExecuteQuery()
Write-Host "receiver removed"
}

 catch [Net.WebException] 
  {
  Write-Host "Failed to delete the receiver" $_.Exception.Message.ToString() -ForegroundColor Red
  }

}


# Paths to SDK. Please verify location on your computer.
Add-Type -Path "c:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.dll" 
Add-Type -Path "c:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Runtime.dll" 

# Insert the credentials and the name of the admin site
$Username="spadmin@xxx.onmicrosoft.com" 
$password = "$xxxx" 
$url = "https://xxxx.sharepoint.com/sites/S046WW16776"
$AdminPassword=Read-Host -Prompt "Password" -AsSecureString
$Url="https://xxx.sharepoint.com/sites/S046WW16776"
$ListTitle="Project Metadata"
$EventReceiverGUID="8ded46d9-6b87-4dac-9532-64d013122e92"

Get-SPOListEventreceivers -Username $Username -AdminPassword $AdminPassword -Url $Url -ListTitle $ListTitle -EventReceiverGUID $EventreceiverGUID