The spelling of the phrase "imprest up on" can be a bit confusing, but it's fairly straightforward once you understand its components. "Imprest" is spelled with the phonemes /ɪmˈprɛst/, with the primary stress on the second syllable. This word refers to a small amount of money given to someone for a specific purpose, often as seed money or to cover initial expenses. "Up on" is simply a prepositional phrase spelled with the phonemes /ʌp ɑn/, and it means "on top of" or "in addition to." Together, "imprest up on" means "in addition to the initial amount of money given."
There is no widely recognized term or phrase "imprest up on" in the English language. It does not have a standard dictionary definition. It is possible that the phrase you provided is a combination of multiple words or concepts, or it may be a specific term used within a certain context or industry. Without further information or clarification, it is difficult to provide an accurate definition for "imprest up on". If you can provide additional context or explanation, I would be happy to try to help you further.