How (not) to use Scheduled Reminders with GoCardless contributions.

Trying to create a Scheduled Reminder that fires on the date of a completed contribution will fail.

Read a longer discussion of the problem if you like but it's because the Contribution's receive_date is always going to be a day behind when the contribution is confirmed by GoCardless, and this means the Scheduled Reminder system will not see it; not trigger.

The time between the charge (receive_date) and the confirmed payment is normally a day. (I'm not sure if it's affected by weekends/holidays also.)

So to use a Scheduled Reminder on a completed contribution you would need to add a gap of at least 1 day after the Receive Date to cover this gap.

Some suggest that CiviRules may help provide a useful alternative to Scheduled Reminders.