1 2 3 
2 3 1 
3 1 2

Do you see all numbers from 1 to 9 there?

No.

All the rules are explained, and the link is there to let you read the rules fully.

About 3.

returns true if it is a valid solution, or false otherwise.

The cells of the sudoku board may also contain 0's, which will represent empty cells. Boards containing one or more zeroes are considered to be invalid solutions.

You should return false when a 0 is on the board, yes. No other rule needed.

Not a kata issue, read this: https://docs.codewars.com/training/troubleshooting#print-input