Is there a way for us (the customer of Synctera) to know if a payment via direct deposit is on its way?

Generally this is not possible but in some cases Payroll providers send the ACH transfer two days early, (i.e they send an ACH transfer on the Aug 29 ACH file to be executed on Aug 31)

For those, Synctera has a new future dated ACH webhook where you can see that the ACH has arrived and will be executed against the customer account in the future. The Webhook has the 'type' ACH.INCOMING.FUTURE_DATED".