VPN not completing after Duo authentication

I’m having an issue where we are using Duo authentication to secure Meraki client VPN. I have the Duo authentication proxy running on a server internally and I have things configured as accurately as I can figure. The issue is that when I connect to the VPN, I do get the Duo push prompt in the mobile app, but when I approve it nothing happens. The VPN connection times out and I am unable to connect. I have contacted Meraki to have them increase the client VPN timeout value to 60 seconds, but this did not make any difference. What else can I check that would explain why the approval is not getting back to the authentication gateway?