By default, any incoming traffic is blocked unless it has a forwarding rule or NAT, which seems to be the case in your case.
You don't need to use software to check this, just check the rules created.
You don't need an additional rule, since L3 rules are intended for outside.
Check the documentation.
https://documentation.meraki.com/MX/NAT_and_Port_Forwarding/Port_Forwarding_and_NAT_Rules_on_the_MX
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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