What triggers QuickBooks Online to send an eCheck?

At a high level, once the check is created correctly in QuickBooks Online – the eCheck is sent automatically. However, at a more detailed level, an eCheck isn't sent until all three conditions below have occurred.

1. The QuickBooks bank account must be linked with your eChecks account. 
2. The payment must be greater than $0.
3. The Print Later box must be selected to suppress the standard printing function for a paper check.

When the system detects these conditions, it initiates the creation of an eCheck – which is then sent to the email address on the vendors profile.  Every 5 minutes QuickBooks pushes to eChecks to be created and delivered.  Do not be alarmed if the check isn't sent out instantly.