A certificate of insurance is how a general contractor knows the drywall sub won't become the GC's claim. It names the insurer, the policy types (general liability, workers' compensation, auto), the limits and the expiry dates, and usually lists the GC or owner as an additional insured. The GC collects one from every sub before the sub sets foot on site, and the GC's own workers' comp audit at year end will ask for them: a sub with no certificate is treated as the GC's employee for premium purposes.
A worked number
A GC pays $84,000 to subs in a year. At audit, $19,000 of it went to two subs with no certificate on file. Workers' comp at a carpentry rate of roughly 8% bills the GC about $1,520 in additional premium for payroll that wasn't theirs, plus the liability exposure if either sub had been hurt.
The mistake it hides
Expired certificates. A COI dated for last year's policy is paper; the coverage may have lapsed the month before the sub got hurt. Track expiry dates and collect renewals, and collect the certificate before the first payment, when the sub still has a reason to send it.
In Obra
Obra has no document storage on vendor records. Put the expiry date and where the certificate lives in the sub's vendor notes, and attach a copy to the sub's first recorded payment on the job so it sits on the job's record when the auditor or the owner asks. Obra doesn't verify coverage; the insurer's agent does.