A hint, for your experiment:

The most effective tests have a number beginning with "9".

901123 sats is a great one.

Also, 989800 sats.

You could do an edge case, like 999999, to check the boundary. Maybe go full 7-digit, to make sure the roll-over is covered. Something like 1234567 is always a classic.

Oh, let's throw caution to the wind. How about 123456789?