Learn Polish: Wprawdzie mam mało pieniędzy, ale muszę się odwdzięczyć. - Admittedly I have little money, but I must return the favor.

The root of this verb is tied to the adjective wdzięczny (grateful). The prefix od- often indicates reciprocation or doing something "back." Therefore, odwdzięczyć się literally means to give gratitude back, which translates naturally as "to return a favor."

I usually use chociaż for "although". How is wprawdzie different here?

Wprawdzie translates more closely to "admittedly" or "it is true that". It is a discourse marker specifically used to concede a point before immediately introducing a contrast. Because of this, it is almost always paired with a word like ale (but) or jednak (however) in the second half of the sentence.

Why do we use pieniędzy instead of the standard plural pieniądze?

This is a quick reminder of how quantifiers work in Polish. Words that express an indefinite amount, like mało (little/few), dużo (much/many), or trochę (a little), require the following noun to take the genitive case. Here, that means using the genitive plural form: pieniędzy.

How would I modify this sentence to specify who I am returning the favor to?

The verb odwdzięczyć się requires the person receiving the favor to be in the dative case. If you wanted to say "I must return the favor to him," you would add the dative pronoun mu: muszę mu się odwdzięczyć.