There are occasional errors in the traditional banking system. Usually, this is the result of a bad account number entry, using the wrong type of account (a brokerage instead of a banking or checking account), or having your bank reject the Swan withdrawal due to triggering some issue on their end.
You should have received an email explaining the source of the error and how to correct it to re-enable your account. Once you update your plan, make sure it says "Active" on your dashboard, like shown below:
If the plan is indicated as paused, then click the "Reactivate" link to re-enable it.
If you need to move the date of your next ACH transfer, you can do so directly from your dashboard. Just select "Edit Plan" and then adjust the next ACH transfer date.