Get a short-lived, order-scoped link into the Get Plus returns
portal. Opening the returned url lands the customer directly in
the return flow for that order — no email OTP and no email address
required — where they can select items, choose a reason and
resolution, and submit the return.

Use this from any integration that has already authenticated the
customer — a storefront, an OMS, or customer-service tooling — on
any platform (Shopify, WordPress, custom, ...). Your system vouches
for the customer; the link carries that trust into the portal.

The order is resolved by order_number within the store your API key
is scoped to. An order that does not exist in your store returns
404; an order with nothing left to return returns 422.

The embedded token grants access to this order's return flow only and
expires at expires_at (about 1 hour). Request a fresh link each
time the customer starts a return, and call this endpoint
server-to-server — never embed your API key in a client
application.