What happens to mid-trial subscribers when I set a plan's trial days to 0?
I want to remove the free trial from some of my Shopify App Pricing plans. I'm trying to figure out what happens to merchants who are *currently* in the middle of a trial when I make that change.
The Shopify docs say:
> If you update your trial periods, then previously consumed trial days are subtracted from the new totals.
Two possible interpretations:
**Existing subscriptions are untouched.** Mid-trial merchants keep their original contract and finish their trial normally. The new trial=0 only applies to *new* subscriptions going forward.
**The subtraction rule applies retroactively.** If a merchant has consumed 5 days of a 10-day trial and I set the plan to 0 trial days, the math becomes `0 − 5 = −5`, clamped to 0 — so their trial ends immediately and they get billed.
Which one actually happens?
I found a blog post from FraudFalcon (wempe.dev) showing that changing a plan's *price* doesn't affect existing subscriptions, but they didn't test trial-day changes specifically. The official docs are ambiguous on this — the "subtraction" rule lives next to the uninstall/reinstall example, which makes me suspect it only applies when a new subscription is created (re-install, plan switch, etc.) rather than to active mid-trial contracts.
Has anyone actually done this and can confirm what Shopify does? Bonus points if you can confirm whether `BillingReplacementBehavior` affects this at all.
Thanks!