AUSTRALIA 1938: 3d blue KGVI, Die II (ACSC 193), earliest recorded use on parcel piece cancelled BRICKFIELD HILL / N.S.W / 23 FE 38.
According to the ACSC, the stamp was printed in August 1937, but issue was delayed until March 1938. This example is, however, clearly dated to late February.
Postage $4 for Australian addresses (includes tracking), $17.50 for everywhere else (registered with signature required).