Actually not required which is why its a scam pulled off by self-centered,selfish jerks that feel their smelly mutt should be allowed in the cabin because it makes “them” feel good .
The entire basis for liberalism, it makes “me” feel good. F every one else.
I’ll beg to differ with you because my wife used to travel with her Service Dog. We had to have a health certificate from the vet in addition to it being noted at the time of sale for the ticket. That document had to be presented to the ticket agent at the airport, TSA and at the gate.