I have received a MS350, I have connected it to a Catalyst 2960. I have set the Meraki port as a trunk and the catalyst port as a trunk too, but the catalyst doesn't show the port as a trunk (when I type show interfaces trunk)
On the 2960:
The config is as follows:
interface GigabitEthernet0/15
description Link to Meraki Switch
switchport trunk allowed vlan 1,30,50
switchport mode trunk
show interfaces gigabitEthernet 0/15 trunk
Port Gi0/15
Mode on
Encapsulation 802.1q
Status Other
Native vlan 1