37 CFR § 1.311 - Notice of allowance.
(a) If, on examination, it appears that the applicant is entitled to a patent under the law, a notice of allowance will be sent to the applicant at the correspondence address indicated in § 1.33. The notice of allowance shall specify a sum constituting the issue fee and any required publication fee (§ 1.211(e)), which issue fee and any required publication fee must both be paid within three months from the date of mailing of the notice of allowance to avoid abandonment of the application. This three-month period is not extendable.
(b) An authorization to charge the issue fee or other post-allowance fees set forth in § 1.18 to a deposit account may be filed in an individual application only after mailing of the notice of allowance. The submission of either of the following after the mailing of a notice of allowance will operate as a request to charge the correct issue fee or any publication fee due to any deposit account identified in a previously filed authorization to charge such fees:
(1) An incorrect issue fee or publication fee; or
(2) A fee transmittal form (or letter) for payment of issue fee or publication fee.