Fill in the numbers in each empty box, so that sum of each 3 adjacent digits is always 15

I was in a couple’s home trying to fix their Internet connection. The husband called out to his wife in the other room for the computer password. “Start with a capital S, then 123,” she shouted back.
We tried S123 several times, but it didn’t work. So we called the wife in. As she input the password, she muttered, “I really don’t know what’s so difficult about typing Start123.”