To create a pfSense site to site VPN, you need to log in to your pfSense #1 HQ and navigate to #VPN / IPsec and click on + Add P1. Set the address of the Remote Gateway and a Description.
Scroll down to Phase 1 Proposal (Authentication).
Now head to any page you like, or this one, to create a Pre-Shared Key.
More info >> https://ibmimedia.com/blog/127/process-to-set-up-site-to-site-vpn-with-pfsense
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