With accent marks:
Долг платежо́м кра́сен.
The beauty of a debt is its payment
This proverb reminds us that we should always pay our debts back.
The word красен here comes from красный (red). In the old times, красный meant красивый.
The closest English equivalent is "One good turn deserves another".
Other Russian proverbs
Fear has big eyes.
Without labor, you can not even catch a fish in the pond.
You can't spoil the porridge with butter.
Get your sleigh ready in summer and your (horse-drawn) cart in winter.
To live a life is not the same (not as easy) as to go through a field.
Hurry to much and you will make people laugh.
The forbidden fruit is sweet.
You see your friends in the times of trouble.