When I flew back to the US from Berlin, I just went and got a $15 antigen 'results in 20 minutes' from an official testing place (they administered it) and used the emailed results to show negative. As long as the email shows the five requirements (name of testing place, type of test, result, I can't remember the others but it's pretty basic stuff) you are good. The whole $$$ "FlySafe" marketing bs is just to scare you into getting the more expensive ones. Flight agents just want to see you tested negative with an antigen performed by a legit center.
Edit: Found it:
Type of test (indicating it is a NAAT or antigen test)
Entity issuing the result (e.g., laboratory, healthcare entity, or telehealth service)
Sample collection date
A negative test result must show the sample was taken no more than 1 day before the flight.
A positive test result for documentation of recovery from COVID-19 must show the sample was taken within the 90 days before the flight.
Information that identifies the person (full name plus at least one other identifier such as date of birth or passport number)