Prefill customer email with better auth integration

[andyluak]

I have a hono BE with everything setup. The below checkout link works fine.

${import.meta.env.VITE_API_URL}/api/auth/checkout/launch-${isYearly ? "yearly" : "monthly"}?customer_email=${encodeURIComponent(session?.user.email || "")}

The problem is that I am unable to find in docs or integration how to prefill the customer email.

Any help would be lovely.