Learn how to say Prepayment correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word prepay:
verb (prepays, prepaying; past and past participle prepaid)
[with object] (usually as adjective prepaid)
pay for in advance:
prepaid licence fees
(as adjective prepaid) (of an envelope or address label) supplied with the postage already paid for contents up to a certain weight.