rate of payment vs repayment rate

rate of payment and repayment rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
rate of payment	Yes	No	No	No
repayment rate	Yes	No	No	No

As nouns, rate of payment and repayment rate are synonyms defined as:

rate of payment and repayment rate: the amount of money paid out per unit time

Other synonyms of rate of payment include installment rate, payment rate.

rate of payment (noun)	repayment rate (noun)
the amount of money paid out per unit time	the amount of money paid out per unit time