The Spanish expression "pagar factura," translates into English as "to pay a bill." The noun "factura" can carry other meanings in Spanish, but with the verb "pagar," the word solely denotes "bill."
There is a verb and a noun in the expression "pagar factura." The verb "pagar" is in the infinitive form, meaning that it does not relay the subject completing the action, but expresses the action itself. The noun "factura" translates into English as "bill" or "invoice." Outside of the realm of accounting, however, "factura" describes the quality of something. In Argentina only, "factura" can refer to a bun or a pastry.