There are many different reasons in many different states as to why a SR-22, certificate of financial responsibility may be required. One common reason is that the person did not have the state required insurance however not the only reason.

Many states require the SR-22 to get your license reinstated even if you had the required insurance at the time of the accident. The reasons for this may vary but in general the state want to verify that the person is being responsible now that their license has been returned. If the license suspension or revocation was for a lengthy period of time States may assume the person's car insurance was cancelled or non-renewed due to the person's licensing status. The SR-22 is one way to make certain the proper coverage is obtained when the license is returned.

It appears that your son may live in Florida from the information you gave. If that is the case then normally the state required car insurance includes Personal Injury Protection coverage ($10,000) and Property Damage Liability coverage ($10,000).

However as the Florida Department of Financial Services (FLDFS) notes, if a person is involved in an accident the FL Financial Responsibility Law, regulated by the Department of Highway Safety and Motor Vehicles, also requires Bodily Injury Liability coverage ($10,000 one person, $20,000 one accident or $30,000 combined) to be purchased.

So though the FL HSMV does not require you to carry bodily injury liability (BIL) in order to obtain vehicle registration, if you are involved in an accident in which the other party is injured, you will be penalized for not having this coverage according to information given from the FLDFS.