Australia
"Contains an Enclosure"

Australia #7B (sealing flap on top 13 mm wide) sent from MELBOURNE (machine cancellation 14 FEB 1955).  

The sender, a stamp dealer, failed to comply with one of the basic rules for aerogrammes. He enclosed something inside the aerogramme (a price list for kiloware, as is revealed by the message on the writing panel).

The admonition on the back panel states "If anything is enclosed, letter will be sent by ordinary mail." The postal authorities detected the enclosure, h/s the aerogramme "Contains / an Enclosure" and diverted the aerogramme to surface mail, which was indicated by crossing out the "By Air Mail" routing instruction.