Why not use the 868L in main router mode then set up DDNS on it?
I personally don't see a need for any AP to have or operate DDNS. This would probably cause other connection problems and if the main host router lost connections with ISP services or goes bad, then your having to troubleshoot more to find the problems. Also having AP so more processing of data like this would probably impact performance. AP are only there to tunnel traffic from connected client devices to the main host router and out to the Internet. It's what Main host routers do and meat for, not APs. Let the main host router handle the DDNS and routing operations. Let the APs tunnel the traffic in which they are designed to do.