HUD

This event gets triggered when a player enters/leaves a vehicleshop, use it in your own script to hide/show your HUD.

RegisterNetEvent('av_vehicleshop:state', function(state)
    if state then
        -- Hide your HUD
        
    else
        -- Show your HUD
    
    end
end)

I don't know what HUD script are you using, ask the person who create it what export or function you can trigger to show/hide it.