I hate Khaki Weed, I really do, so much so that at one stage I had it almost eliminated from the footpaths of the small village I live in and despite my slackness over the past couple of years numbers are still low and just the other week had to spray the footpath between the car park and my local gym (yes, I do go and stop laughing).
Khaki Weed (Alternanthera pungens) is a low growing groundcover with spiny burrs, active in summer, particularly after rain, it’s spread by car tyres, shoes and animal hoofs.
Selective herbicides are effective against it while leaving the grass alive (avoiding big dead patches in your lawn), with dedication they can be chipped out and binned), steaming and “organic” herbicides may work but will leave a large dead patch.
Image from: https://weeds.brisbane.qld.gov.au/weeds/khaki-weed
Further information
https://weeds.dpi.nsw.gov.au/Weeds/Details/75