Did you searched the internet before you posted here?
Because with google, you will find many similar issues and a high percentage points to a weak battery.
1] Although your battery is only 8 months old it can fail or simply has not enough juice/is drained.Therefore don't skip to test it. Think logic.
2] You wrote: I needed to remove something that previous owner had installed.
So you fiddled with the electric configuration. Fair chance you did something wrong with it?
Or the former owner did stupid things and now after you removed something it became a problem.
3] Maybe somewhere there is a bad connector? Check connectors and mass cables.
4] Then was there a number with the airbag message?
5] Did you also checked with an OBD device? If so copy the exact full info with it.
6] Could you start the car and have you made a few miles?
7] Did the airbag message came back or did it stay away?