A confirmation before adding a product billed at a longer period

For a product that needs no shipping, such as a membership or a digital good, a contract could end up billing that product's full price on every cycle even when every one of the product's own plans is meant to deliver it less often, for example a yearly product added to a monthly-billed line. This produced a real overcharge: one shopper was billed a yearly product's full price every month.

Adding a product like this to a contract, or swapping a line to one, now checks whether every live plan on that product delivers more slowly than the contract bills. If so, the merchant sees a warning naming the mismatch before the change goes through, with an explicit "Add anyway" to proceed if that's intended.

This only affects a no-shipping product whose plans deliver more than 10% longer than the contract's billing period; a normal product swap or add is unaffected.