I have already come up with 50 ways that a management company can screw you for profit without you ever knowing(or not finding out for awhile). Did you have an inspection before you made an offer on the property? Do you have a picture of the property you bought? How do you know if that picture shows the house you actually own? or if it even hows the ‘current’ state of the house you own?
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.