On the customer's network, a TP-Link router is deployed and PPTP is configured at the remote end. However, the intermediate AR160-S blocks PPTP packets. As a result, the connection fails.
Allow PPTP packets to directly pass through without being processed.
CLI: Run the nat alg pptp enable command to enable the function.
Web: Choose IP Service > NAT and select PPTP next to ALG configuration in the Global Settings area.