Wikipedia describes payload as,
Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight.
payload 1930, from pay (n. or v.) + load (n.). Originally the part of an aircraft's load from which revenue is derived (passengers, cargo, mail); fig. sense of "bombs, etc. carried by a plane or missile" is from 1936. Online Etymology Dictionary, © 2010 Douglas Harper
However, Google n-grams has some results from earlier, like this one from Automotive Industries, Volume 30, Chilton Company, Incorporated, supposedly 1914, page 976:
dead weight of not more than 3,500 kilograms, and the heavy trucks, whose dead weight could be 5,500 kilograms, were both to carry a load of at least 2,000 kilograms, and with the aid of trailers should transport, respectively, a payload of 8 and 15 tons more.
or page 1338:
HERETOFORE the Prussian army administration has wanted for military transportation work only motor trucks capable of carrying a payload of 5 to 6 tons
or Vol. 22. page 721,
The tilt should be adjustable with relation to the direction of the propeller shaft and the whole power plant and the payload.
suggesting that the word was used earlier. One starts to wonder, whether this is a military terminology, and how did the usage later developed, whether the boom around the '55-65 as seen on n-grams is a result of (literal) rocket science or rather computers (later networking?) or something else.
Are there more information about how this word was coined and how did it develop?