Site-to-site VPN with on-prem environment

Hi,

Last week I was asked to create a site-to-site tunnel between an azure VM and the on-premise network (domain controller) I administrate.
I managed to create a gateway with a public IP and the initial local-site settings for the tunnel.

Now I get the following:


Which isn't surprising since a VPN tunnel needs a proposal to match on both sites. However there is no way to change the IKE and IPSEC settings in the azure GUI.
I tried to find the preshared key via powershell but I keep getting the following errors:

I can login with Login-azureRmAccount and I can find the subscription ID viaSelect-AzureRmSubscription, but when I try to set the default description.
Select-AzureSubscription -Default -SubscriptionId gives the following error:Select-AzureSubscription : The subscription id <subid> doesn't exist.

I'm feeling like I am running into a license problem of some sorts, since I can manage the azure VM, but my subscription is denied when I'm trying to set up a simple VPN tunnel.

Can anyone confirm I'm wasting my time trying it this way? Is there an easier way? I just need to get the proposal parameters, including the preshared key, to set this thing up.

Thanks,

Tim