Validating a certified payroll SaaS for small subcontractors ...anyone built in this space?

Validate around withheld payment, not generic compliance. Ask each subcontractor to walk you through the last certified-payroll submission: who prepared it, which form or portal was required, what caused a correction, how long approval took, and whether payment was delayed. The strongest wedge may be a job-level checklist plus error detection for one jurisdiction before adding full payroll. A paid pilot is credible when it prevents one rejected report or shortens one payment cycle.