It is not a deep "brain-stem test." Can't use that for an excuse.
You need to talk with the testing companies; Bon Gove and the Airlines are irrelevant. If the testing company won't give you a negative-test written good-for-travel certification, you lose. Buy another antigen test. I actually asked BonBida why I could not get a negative Day 5 test result even though I had paid for the test; they responded, "the nurse told you that you will only get to hear from us if you are positive. Because it is just a check and not for travel, we will only contact you if it is not good." not an acceptable ansser, but I was just trolling a bit.