Cannot create a private endpoint for a storage

Hello,

Background:

A storage account has been created on Azure, with a file share.

Firewalls and virtual networks is set to "Enabled from selected virtual networks and IP addresses"

Goal:

Give access to the file share from on-Perm network.

I was trying to create a private endpoint  ,  in the "Virtual Network" step , chose the gateway subnet but I got 2errors:
"The selected subnet 'GatewaySubnet' is restricted and cannot be used with a private endpoint""The selected subnet only has capacity for 0 private IP address(es), while the selected sub-resource requires 1."

Noe sure where I can increase that capacity !