Mint a tracked subscription link

Turns a quoting session into the tracked link handed to the traveller. The first call of a session creates a quoting-stage subscription with your affiliate reference baked in server-side and returns the URL that resumes it; every later call of the SAME session returns the SAME subscription: a repeat offer click replays it (200, replayed: true), a changed trip updates it in place (updated: true), and a different session can never reach it, so two travellers with identical trips can never share a link. One exception protects the traveller: once they take the subscription past quoting (presubscribed, paid, subscribed), it is frozen, and the next call of the session rolls onto a fresh subscription (201, new subscriptionId) that the session follows from then on.

sessionId is REQUIRED and comes from the POST /quotes response; a fabricated value fails its HMAC with BAD_SESSION_ID. Pass the offerId the traveller clicked to land them straight on the presubscribe form with that offer selected at the live re-rated premium (the funnel falls back to the offer list when the offer no longer prices); without it the link lands on the offer list.

The affiliate reference lives on the subscription rather than in a query string, so attribution survives a copy-paste through a messaging app, an email client and a browser redirect, and cannot be forged.

With a sandbox key (ak_test_), no real subscription is created, so there is nothing for the link to resume. subscriptionId is a placeholder (sub_sandbox_...), ref is null, and url opens the HelloSafe quote form with only the residence country, destinations, number of travellers and trip intent prefilled: never the dates or the ages, and never the subscription step, even when you pass an offerId. The prefilled subscription step (/travel-insurance/app/subscribe?subscription_id=...&offerId=...) only exists with a live key (ak_live_).

Warning: the sandbox link opens the real hellosafe.com funnel. There is no test card and no sandbox checkout, so any payment made through a sandbox link is a real purchase with a real card. Testing the payment step end to end means making a real purchase through a link minted with your live key.