'Do' and 'does' are both equally forms with the current indefinite tense in the verb 'to complete.' Which a single you are going to use will largely rely on the sentence's topic. Their usage is almost similar, apart from 1 instance where You should use 'do' and not 'does.' https://financefeeds.com/can-new-copyright-project-spacepay-replace-traditional-pos-systems-heres-why-some-think-so/