I sent a message asking about test requirements to the contact email on the government page , but they've not responded. The word "certified" is used, and I wanted an explanation of that.

A US citizen posted in a Facebook group that she was denied entry because her test was considered invalid, since it said "no evidence" rather than "negative". She also said that they told her the test had to have a raised seal. She had arrived on a charter flight, and frankly, I think the problem was that she arrived from the US and not the test. Unfortunately, there's no further information from her, as she left the group after a few people in the group were pretty nasty to her.

I agree that there needs to be much more clarification.