When you write "For each VPN gateway in the subnet" it is better to indicate how to find the VPN gateway in the subnet.
In my code, I found the relevant VPN gateway with resource-group id.
cmd = f"ibmcloud is vpn-gateways --resource-group-id {resource_group_id} --output json"
Delete all VPN gateways in the subnet, if any
To list all VPN gateways in your account, run the following command:
ibmcloud is vpn-gateways
For each VPN gateway in the subnet you want like to delete, run the following command, where $vpnid is the ID of the VPN gateway.
When you write "For each VPN gateway in the subnet" it is better to indicate how to find the VPN gateway in the subnet.
In my code, I found the relevant VPN gateway with resource-group id.
https://cloud.ibm.com/docs/vpc?topic=vpc-deleting-vpc-resources&interface=cli