Okla. Stat. tit. 61, § 61-123: Supervisor's certification to accompany invoices -

Exception.

A. All statements or invoices submitted to the awarding public

agency for work performed shall contain a certification by the

supervising architect or engineer, or other supervisory official if

no supervisory architect or engineer is employed for the project,

that work for which payment is claimed has been performed and that

such work conforms to the plans and specifications for the project.

No such statement or invoice shall be paid by the awarding public

agency without such certification. The execution of a certificate,

as herein provided, shall not constitute a defense or in any other

manner affect any cause or causes of action which the awarding

public agency might otherwise have against the contractor for

nonperformance of a public construction contract.

B. If project progressive payments are based on the public

agency’s estimated quantities of materials provided and work

performed, certifications are not required. Payment of progressive

estimates shall not constitute a defense or in any manner affect any

cause or causes of action which the awarding public agency might

have against the contractor for failure to properly perform in

accordance with the project contract, plans, specifications, or

special provisions. Final estimates shall contain a sworn

certification signed by the contractor that the work performed and

the material provided conform to the requirements of the contract,

plans, specifications, and special provisions.