Most, if not all, carriers have the right to ask to see a government-issued ID throughout the journey or before you board the bus.
Government-issued ID may be a passport, a driver's license, or even a health care card. It is important that the ID has a photo of you and also your details.
If for any reason you do not have an ID or your ID has expired, call your carrier directly to see if they can set you up with some sort of password in order to board.
Please see a list of carriers' phone numbers here: https://www.wanderu.com/en-us/carrier/