I encountered this sentence in an article from NHK News web easy:
今まで国からお金をもらうためには、旅行した人が本当に利用したことがわかる書類などを「Go Toトラベル」の事務所に出さなければなりませんでした。
I cannot understand what 「本当に利用したことがわかる書類」means in this case. Ignoring that part the remaining part of the sentence can be translated as: "Up until now in order to get money from the government, people who have travelled, have to send [missing part here] to the 「Go Toトラベル」office".
Now, I know that 利用する means "To use", and by inferring things, maybe, that part can be roughly translated as "the documents that do really certify that they were on a trip", but I'm not sure and I cannot see how「本当に利用したことがわかる書類」carries that meaning.