On PS Form 2976-A, Customs Declaration and Dispatch Note — CP 72, the mailer must include an ITN or AES Downtime Citation (see 520) in block 10 and a license number in block 16.
On PS Form 2976-B, Priority Mail Express International Shipping Label and Customs Form, the mailer must include an ITN or AES Downtime Citation (see 520) in block 3 and a license number in block 14.