Can I use another currency besides for USD?

Yes, you can do this from the settings of the payment integration.

First, you should click on the integration and then click on "Payment Settings". Then you should just edit the "Currency" field. Please refer to the attachment.

Let us know if you need any further assistance.

Thanks. This is what I get when I click on payment settings. The currency cell is not editable. 

(I'm using the free version).

Actually, you were trying to edit the settings of a particular product from the payment integration. It is normal that the currency is not editable from there.

Can you please try to follow the guide below:

Let us know if you need any further assistance.