Spotify Connect between to Networks

[Kuddel071089]

Hello,

first a lot of information:

home-network: 192.168.4.0/24

guest-network: 192.168.5.0/24 VLAN 5

yamaha-receiver: 192.168.4.9/24

router / firewall: sophos

my smarthphone os: Android 8

my guest at home are using an own network, where only the internet is unlocked and the connection to my yamaha receiver.

while using the guest-network, the connection to the internet works without any problems.  the access to the yamaha webserver is possible too.

when i'm starting the Spotify App (in the guest-network), it isn't possible to connect to the receiver. it is only possible in the home-netzwork

Have someone any idea to solve this problem?