Diego,123,
The answers provided are the same that I would be telling you. You will need two identical MX's in order to setup for failover. The documentation for this can be found here:
Re: How to connect two meraki MX for redun dancy - The Meraki Community
One thing to keep in mind is that each Meraki device needs a license to work and you will need to create an account on the dashboard. To set this up go to dashboard.meraki.com and from there you can claim your equipment and add the licenses.
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