Web-email-handoff
Web-email-handoff is the pattern Syndik8 uses to upgrade a free syndicate on iOS and Android. Apple’s and Google’s store rules forbid in-app calls-to-action that route payment outside their stores, so the mobile upgrade prompt cannot offer a direct checkout button.
When an active admin attempts an action beyond the free-plan limits, the app shows the limit and the service sends that admin a factual action-limit notice, subject to a per-syndicate cooldown. The email identifies the failed action and links to the authorised Subscription screen under /web/subscriptions/, outside app-claimed paths. It does not promote an offer or open the checkout directly. Signing in, if necessary, preserves that browser destination.
There is no in-app button to request the email. On the web screen the admin may manage the subscription; starting checkout requires an explicit early-start request, followed by Terms agreement on the checkout page. Installed-device verification of the full browser/authentication link chain remains a release check.