Learn French: Vous ne pouvez pas entrer sans payer. - You cannot enter without paying.

In English, we use an -ing verb after prepositions (without paying). In French, almost all prepositions, including sans, must be followed by the infinitive (the unconjugated dictionary form). So, without paying translates directly to sans payer.

Why is entrer also in the infinitive?

This follows the double-verb rule. When two verbs are used together for the same subject, only the first one is conjugated. Here, the first verb is pouvez (conjugated for vous), so the second verb entrer (to enter) stays in its infinitive form.

Does Vous ne pouvez pas mean you cannot or you may not?

It means both! The French verb pouvoir (can / to be able to) is used to express both physical ability and permission. In this context, it means you do not have permission to enter.

Is vous referring to one formal person or a group of people here?

It could be either! Vous is used when speaking formally to one person (like a customer or a stranger), or when addressing a group of people. The French sentence is exactly the same in both cases.