Lyft has rather high requirements for passenger vehicles that are based strictly on the underlying city or state requirements. First of all, they must have at least 4 doors and from 5 to 8 seat belts (including the driver’s seatbelt). Lyft also has certain requirements for the age of the car, depending on the state you are to work in. Make sure to check this aspect.
As for the restrictions, taxis and limousines are not allowed in the service, as well as a whole list of small cars (subcompact vehicles). The problem with the latter is that they do not provide the proper level of passenger comfort in view of the compactness of their cabin (some existing drivers, however, are still using such cars in the service due to this restriction having come into effect in February 2019; they aren’t able to add an extra vehicle of such kind, however).
You can always check the status of your driver application online, and if your car needs some inspection and repairs, see the inspection form according to your state. And if you do not have your own car – Lyft’s Express Drive will help! It is a specialized rental service to help you start earning right now.