The first know use of $0$ as it's own number was in India, but what was the equation in which it was used? Also, what was the tablet/scroll/whatever about?
I touched upon this in my answer here, near the end.
This source indicates that one of the earliest known instances - if not the earliest known instance - is a carving on a tablet discussing gardens in the town of Gwalior. The page says:
We have an inscription on a stone tablet which contains a date which translates to 876. The inscription concerns the town of Gwalior, 400 km south of Delhi, where they planted a garden 187 by 270 hastas which would produce enough flowers to allow 50 garlands per day to be given to the local temple. Both of the numbers 270 and 50 are denoted almost as they appear today although the 0 is smaller and slightly raised.
This shows images of the tablet and gives the inscription as
Om. Adoration to Vishnu! In the year 933, on the second day of the bright half of the month of Magha the whole town gave to the temple which Alla, the son of Vaillabhatta, had caused to be built a piece of land 270 hastas in length and 187 hastas in breadth, for a flower garden the town gave in perpetual endowment for a daily gift of 50 garlands of flowers.
While the tablet is from 876 A.D. yet refers to a year 933, this is explainable because the ancient Indians did not use the A.D./B.C. calendar used widely today.
Amir Aczel has a new book ["Finding Zero"]. There he finds zero on an inscription from 7th century Cambodia. Perhaps this is earlier than in India.
(My remark copied from that other question.)
The use of zero in India must be a lot older than the inscription from AD 876 mentioned by HDE. The use of the "Indian numbers" and specifically zero was introduced into the Muslim world by al-Khwarizmi, who died about AD 850.And he had them from some Indian text.
I am surprised that no one has considered the number of times that the zero is used in the 5 books of Moses in the Hebrew language, which were written down by Moses in about 1273 BCE, as being even older that India or anywhere else. And considering that the first 11 chapters far predate the Hebrew people and Abraham, then you can push that date back maybe another 2000 years at least. In Genesis chapter 5, the first clear use of zero is used for how old people were when their first sons were born and how long they lived, we see that zero is used 14 times! And by the way, archeology continues to validate the historicity and dates given in Genesis.