。
I earn 100 euros a day.
Literal
I [topic-は] one day [per-に] 100 euros earn [polite-ます].
The に in 一日に is the distributive 'per' — 'per day,' 'per person,' 'per hour.' This is one of に's broader uses beyond marking location or target. ユーロ is the katakana borrowing for the currency. Otherwise a structurally simple SOV sentence.