@Andrea Longhitano Thanks for reaching out. If your APIM instance is deployed in an internal virtual network, it is not accessible from the public internet. As per this https://learn.microsoft.com/en-us/azure/api-management/private-endpoint you can't use private endpoint if your APIM is deployed inside a VNET, you can use one or the other.
A private endpoint for APIM is typically used when you want to access your APIM service from within your virtual network, while keeping the traffic within your virtual network. This can be useful if you have other services or resources in your virtual network that need to access your APIM service, or if you want to ensure that traffic to and from your APIM service stays within your virtual network.
do let me know incase of further queries, I would be happy to assist you.