Thanks for A2A,
I am configuring my Azure APIM service as internal inside VNET & I am integrating it with Azure Application Gateway. Thing is I didn't get which DNS to configure for Custome DOmain setting Public DNS or Private DNS zones.
Based on Create a public IP address for the front-end configuration, you should configure Public IP and Configure the front-end IP with it.
$publicip = New-AzPublicIpAddress -ResourceGroupName $resGroupName -name "publicIP01" -location $location -AllocationMethod Dynamic
$fipconfig01 = New-AzApplicationGatewayFrontendIPConfig -Name "frontend1" -PublicIPAddress $publicip
And once the gateway is created, you need to CNAME the API Management proxy hostname to the public DNS name of the Application Gateway resource.
So you can choose public DNS based on the official document.