Enable inbound wireguard interface when connected to VPN

I have an AR750 router. I run PiVPN on a raspberry Pi serving Wireguard which I use to allow my mobile devices to access my home network remotely.

When I connect my router to my VPN provider - Mullvad (Wireguard), Iam no longer able to connect my mobile devices to my PiVPN wireguard server/peer.

How do I configure my router to enable my wireguard server to connect externally whilst routing other traffic through the Routers Mullvad VPN connection?

Thanks for your help.

Do you need to open both the wireguard server and the wireguard client?

Hi

Yes. If I am understanding what you mean.

My wireguard server is on a raspberry pi. I want to be able access have the interface between this server and my mobile phone open, whilst the router has the wireguard client enabled and routing internet traffic to Mullvad.

somehow I need the UDP port that my wireguard server (raspberry Pi) uses to not be affected by enabling the vpn on the router.