I don't know if I understood correctly, but, yes, you can create a webhook to get alerts when the public IP of your MX changes.
Navigate to the Network-wide > Alerts page.
When defining an HTTPS server to receive the webhook alert, you have an option to select a payload template.
Click on the ‘Add or edit webhook templates’ to begin. To create a new template, press the ‘Create template’ button.
The template must be written in a way that it renders to valid JSON RFC82591. You can use the ‘Generate Preview’ button to check for any JSON & Liquid syntax errors.
Webhooks support all configurable alert types available in the dashboard under Network-wide > Alerts. You can set the alert type to notify you when the public IP changes.
Webhooks - Cisco Meraki
Meraki webhooks and sample webhooks schemas. - Meraki Webhook API docs - Cisco Meraki Developer Hub
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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