Work through this list:
Payments — charges and payouts enabled? Continue Stripe onboarding if not.
Widget — linked to a campaign and saved?
Campaign / widget fundraising — not paused?
Plan / Stripe mode — if you connected Stripe test mode, live cards will fail. Connect a live account for production.
Amount — ACH widgets enforce a minimum (default $500). Card forms need a valid amount.
Browser — try another device; some banks decline repeated test cards.
Failed attempts appear under Donations (failed/pending) and in Reports → Failed / pending donations. Open the gift for the status Stripe returned.