Between daycare invoices and a toddler who thinks blueberries are currency, I notice every missing dollar. It's not rude; it's responsible. You paid for them when their card failed, now they owe you. Keep it short so you don't spiral.
Text: 'Hey, following up on the trip—your part was $125. Can you send it by Friday?' If they say they're tight, fine, 'Two payments over the next two Fridays works.' Always put a date; otherwise it drifts forever. I send the request in the app and the text at the same time so there's no confusion.
Reminders: one nudge after a week, then one firm message the week after. If nothing after two reminders, stop spotting them and say so next time: 'Can't cover you—still waiting on the last one.' I don't let it sit past that, because the mental load is already full.
