A mid-market retail chain. 38 stores. Deputy for rostering, Xero for payroll. Both configured by competent people.
July rate change comes through from the FWC. The base rate gets updated in both systems. Deputy updates the Sunday penalty display rate it uses for scheduling cost projections. The payroll team confirms the base rate in Xero is correct. Everyone moves on, because as far as anyone can tell, both systems now reflect the new rate and the job is done.
It wasn't done.
The Xero pay item for "Sunday Casual" was a flat dollar amount. Not linked to Deputy. Not derived from the base rate. Just a number someone typed in when the pay item was first created, sitting there unchanged while everything around it moved. The display rate in Deputy shifted. The actual pay rate in Xero didn't.
$2.40 per hour. That was the drift.
Across roughly 320 Sunday casual hours per week, across 38 stores, for 14 months, that $2.40 compounded into approximately $47,000 of underpayment exposure. Not catastrophic for a chain that size. But the kind of number that gets attention from a board, and from the FWO.
Both systems were correct. That's the part worth understanding. Deputy had the right rate for display purposes. Xero had a valid pay item with a valid formula structure. Audit either system in isolation and you'd sign off. The error didn't live in Deputy. Didn't live in Xero. It lived in the handoff between them, in the assumption that when one system updated, the other would follow.
Nobody owned that assumption.
Operations managed Deputy. Payroll managed Xero. Each team trusted that the other had it covered, and neither had the tools or the training to verify what the other team's system was actually doing, because that verification sits in a space that doesn't belong to anyone's job description.
How was it found? A pre-payroll variance check that compared the Sunday casual rate in Xero against the derived rate from the current award base. Flagged in under three minutes. The same check that would have caught it in July, had it existed in July.
I hear this pattern constantly. Not this exact scenario, but this exact shape. Two systems. Both individually correct. Producing an incorrect outcome because nothing governs the space between them. The rostering system says one thing. The payroll system says another. Nobody compares the two.
The casual working Sundays didn't notice. Her payslip showed a rate. She didn't cross-reference it against the Retail Award's Sunday casual penalty calculated on the loaded rate. The pay run balanced. The BAS lodged. The monthly P&L looked normal. Fourteen months of underpayment, building itself one quiet pay run at a time, and the only reason it stopped is because someone finally looked at the gap.
The real problem wasn't Deputy. It wasn't Xero. It was that $2.40 between them that nobody was watching.