How to register static routes for an Asus Merlin and DDWRT?

Question

network hardware

Given:
side A (asus merlin): network 192.168.1.0/24, L2TP Internet, issues ip to vpn clients from its subnet.
side B (ddwrt): network 192.168.2.0/24 Internet PPOE, receives ip from a VPN server from network A.
On Merlin, I registered static routes both in routes and in a separate tab of the VPN user, the routing table does not change. You bring everything in with handles - everything works, but until the first tunnel falls off.