How to forward multicast through an access point to an IPTV set-top box?

Question

ZyXEL

Good afternoon. There are 2 routers, both keentic lite 3, one in router mode, the second as an access point. A TV set-top box (Dune HD tv-102) is connected to the access point via a cable. Question: why does the multicast not reach the set-top box? Problem: does not show a picture and sound, but reads text information from packets.