Prior to this bug fix partial month payroll would require you to have a valid contract which would cover start or end date of the payroll period. This means you can have payroll window (period which was not worked and is not covered by the contract) at the beginning or end of the payroll period, but not both.
You have contract for the period 2016-01-10 .. 2016-01-25.
You try to generate payroll for January (2016-01-01 .. 2016-01-31).
Contract is not covering the start (2016-01-01) or the end (2016-01-31) date of the payroll period.
Payroll generation would fail.
After the bug fix we now can successfully generate the payroll.
— Myk Kyryk, PayrollHero Engineering Team