Selective routing

[BogusBogey 0]

For outbound VPN connections I'd like to establish selective routing. Say to the USA for Netflix on VPN Client 1 and to the UK with VPN Client 2 to watch BBC.
About a year ago I went through a lot to get this working on a RT-AC68U and every single time both routing tables were the same. I've never been able to fix it.
BUT as of today I'm using a new router, an Asus RT-AC87U and I still can't get it working. The problem must be behind the keyboard, right?
There are no scripts installed, just a brand new router with two AirVPN clients.
However, I gave it another shot. Instead of AirVPN, I gave it a try with vpnbook. Guess what? Two simultaneous OpenVPN clients!
I gave it another go with PureVPN test account and also this time it's working. Same goes for NordVPN, also works.

The differences between the three are:
VPN Provider:                AirVPN   - vpnbook       - PureVPN
Protocol:                         UDP - TCP           - UDP
Extra HMAC authorization: Outgoing    - Disabled      - Outgoing
Accept DNS Configuration: Exclusive   - Disabled      - Disabled
Encryption cipher:        AES-256-CBC - AES128-CBC    - AES-256-CBC
Compression:                 none     - adaptive      - adaptive
Custom:        remote-cert-tls server - fast-io       - route-method exe
                        route-delay 5 - route-delay 2 - route-delay 2
               explicit-exit-notify 5 - pull          - explicit-exit-notify 2
                                      -               - mute 20
                                      -               - auth-retry interact
                                      -               - ifconfig-nowarn

I don't know how to get this working with AirVPN, hopefully you can help me?

Thanks in advance,

B.