meraki rules are a little different than the classic "open on top of a deny all" rule set. I usually use the following structure:
allow <protocol> <source subnet> <src port> <destination subnet> <dst port>
deny any <source subnet> src port any destination <10.0.0.0/8,172.16.0.0/12,192.168.0.0/16> dest port any
be really careful with your default deny rule at the end