If you've downloaded the Postscript App via Shopify, you will receive all billing and invoices through Shopify.
You will be billed at the end of the month cycle - but may receive invoices during the month when you change plans. If you are changing plans, Shopify will prorate your plans to reflect how long you were on each tier. If you would like an overview of our tiers and upgrading/downgrading, that information can be found here.
Example: You spend 15 days on the $100 plan, then upgrade halfway to the $200 plan with 15 days left in your billing cycle. Your invoice would show $150. ($100 for your original plan and $50 for the upgrade with 15 days left).
If you have questions regarding your bill, it's best to reach out to Shopify directly.
Any other questions you might have, feel free to reach out to our team via chat!