It shouldn't work with floats. If floats ar needed return must be changed from int to float

I can't get it:

//1..9 = (9 * 1) = 9

//10..99 = (100 * 2) = 200

//100..999 = (1_000 * 3) = 3_000

//1000..9999 = (10_000 * 4) = 40_000

//10_000..99_999 = (100_000 * 5) = 500_000

//100_000..999_999 = (1_000_000 * 4) = 6_000_000

//1_000_000..9_999_999 = (10_000_000 * 7) = 70_000_000

//10_000_000..36_123_011 = (26123011 * 8) = 208_984_088

//sum: 208_984_088 + 70_000_000 + 6_000_000 + 500_000 + 40_000 + 3_000 + 200 + 9 = 285_527_297

//And solution is telling 277_872_985

What am I doing wrong?

If you have set declare(strict_types=1); php would throw an error (because you try to return string as int), if this declaration is missing it will convert string to int.

I've changed assert types, should be fine now, thanks