When Should You Start Worrying About Getting Paid?

Just today I had to send a reminder for payment for the first time. The rules/guidelines presented here would have been a real time saver.

But I'm missing some steps here. Rather than immediately urging payment start friendly and become more strict after multiple messages. From now on I plan to:

1) Remind friendly over phone (informal)

2) Send formal reminder some time after

3) Send payment reminder with listed consequences.

4) Send final warning

All the while logging each step in case things don't work out.