When a backer's payment cannot be collected, their pledge is displayed with an errored status in your Backer Report. You can sort your Backer Report by "Errored pledges" if you'd like to send them each a message with a reminder to fix their pledge (here are the steps they should follow).
We'll also send these backers an email with instructions to fix their pledge, and they'll receive periodic email reminders throughout the following week. They can also fix their pledge by logging into their Kickstarter account and clicking on the "Fix Payment" banner at the top of the page.
Backers with errored pledges will have 7 days from the project's deadline to update their payment method. At the end of this period, we’ll automatically try to collect their pledge again. If this attempt also fails, these backers will be dropped from the campaign and it will no longer be possible to collect their pledge.