How usageCharge works? When to charge?

[captainzero]

My app going to use usage based billing.

Eg: Assume, If merchant has greater than 10 orders then charge $10, if merchant has greater than 20 orders then charge $20.

When to send usageCharge to shopify? I've 2 options in the mind, please suggest the right way.

1. When merchant hitting 11th order then send $10 usageCharge request to shopify, if the merchant hits 21th order within in the same month, then what should I do? I have to send the $20 usageCharge? So the total usage charges will be $30?

2. Count the 30th day from the installation date and count the total orders then send usageCharge request to shopify

Any help appreciated

[captainzero]

Got another idea, I don't know usageCharge works this way.

1. When merchant hits 11th order then post usageCharge of $10

2. When merchant hits 21th order within the month, then post usageCharge of $10 ($20 - $10 (already charge for 10 orders))

How does it sound?