Learn Polish: Zainwestowaliśmy w tę akcję charytatywną cały nasz czas. - We invested all our time in this charity campaign.

With verbs showing involvement, investment, or belief (like inwestować w - to invest in, or wierzyć w - to believe in), the preposition w always takes the Accusative. Think of it as directing your time, energy, or money into the campaign, rather than just being physically located inside it.

Why is it tę akcję instead of tą akcję?

Tę is the strictly correct feminine Accusative form of the pronoun ten (this). In casual, everyday speech, you will often hear native speakers use tą (which is actually the Instrumental form) instead of tę. However, at a B2 level and in standard written Polish, you should always use tę for the Accusative.

The word akcję looks like the English word "action". Is that exactly what it means here?

Not quite! While akcja can mean physical action (like an action movie - film akcji), in Polish it is very frequently used to mean an organized campaign, drive, or initiative. A charity campaign or fundraiser is almost always called an akcja charytatywna.

Why is the direct object (cały nasz czas) at the end of the sentence instead of right after the verb?