If you do not have a Cash App account and are receiving messages from 28581, it is almost certainly a fraud.
If you are an active Cash App user and receive promotional messages about new bargains or hot discounts, it is a Cash App promotional text. However, you must use caution in this regard. They may occasionally request money or OTP codes from you. In that instance, they are attempting to defraud you.
Finally, if someone is sending you messages to obtain your login information, it is a fraud.