Did you mean to use expiry rather than expiration? OED says that this adjective is now “rare.” Last citation is mid-19th century.
The OED is not worth consulting on this, since the letter E dates back to the late nineteenth century. Expiry is perfectly standard American English (I don’t know about UK).
The “rare” label applies only to its use as a synonym for death, not for the expiration of a period, contract, etc. (And it’s a noun, not an adjective.)
Agree with ADB, I used to work at a journal subscriptions agent where the word was used every day in correspondence. I used to think that ‘expiration’ was an Americanism?
Just for fun, did ‘transpiry’ ever exist? Don’t sweat it though…