Translation:The theater needs money to improve.
I think this is an example of where the literal translation in which you translate a verb for a verb, is not fully accurate for communicating the meaning, because it's not as natural a construction in English. It sounds much more natural in English to use the nouns "improvement" or "improvements".
This is common in translating languages, in that in one language you might use a verb's infinitive, but you might use a related noun in the other language, more commonly.
I personally think it's better to think more holistically...i.e. to translate this "needs money for improvements"...this is the approach that tends to read more naturally when translating texts, and also leads to better communication when translating for people in conversation. So I wish Duo would accept this. You could always suggest it if you think it is correct! I notice DuoLingo often accepts non-literal translations, and it may be that they just didn't think of this possibility yet here!