I’m having the same problem as the original post but I do have an external IP.

Slate router, Mango 3.026, connected to fiber modem via Ethernet.
GL UI reports the IP address as 42.xxx.yyy.zzz. Gateway is 42.xxx.yyy.254.

DDNS gl-ddns 3.0.21: installed and enabled: pnXYZ.glddns.com

DNSWireGuard Server 4.14.63/20181119 running and using default settings.
Client setup using default settings: 10.0.0.2/32; listen 8521; DNS 64.6.64.6,

WireGuard iPhone Client 0.0.20190609.
Add a Tunnel: Client settings transferred to iPhone using QR code; no edits.
Endor: 42.xxx.yyy.zzz:51820; 10.0.0.2/32; Listen 39877; DNS 64.6.64.6

  1. Client settings IP
  • WG Client not connected (cellular, WiFi off): data flows ok
  • WG Client connected (cellular, WiFi off): no data flows
  1. Edit Client settings to DDNS address pnXYZ.glddns.com:51820
  • activate WG Client: error— DNS resolution failure…
  1. Delete Client settings. Reinstall via QR:
  • WG Client not connected (cellular, WiFi off): data flows ok
  • WG Client connected (cellular, WiFi off): no data flows

Any advice?

Note: OpenVPN server and client work correctly using default settings.