How to invoice customers and charge for post-booking add-ons

The booking is rarely the final number. The client books a 60-minute session and stays for 90. The car rental adds a GPS at pickup. The consultation turns into a consultation plus a report. The money owed at the end of a job is often more than the money agreed at checkout — and collecting that difference is where a lot of service businesses get sloppy, chasing it over text or just eating it.

This guide covers the clean version: how to change a booking after it's been made, and how to invoice the balance through whichever channel fits — Stripe online, a manual PDF, or Shopify.

Step 1: Add the post-booking charges

A booking becomes an order the moment it's made. That order is editable after checkout, which is what makes post-booking charging possible at all.

The cleanest way to add a charge is an add-on — an optional extra attached to the service. Add-ons aren't only a checkout upsell; you can attach them to an existing order when the work changes. A deep-conditioning treatment the stylist talked the client into, a child seat added at car pickup, an extra hour on a studio rental — each is an add-on line on the order, with its own price and quantity.

Once the add-ons are on the order, the amount due goes up. If the customer already paid the original total at checkout via Stripe, the order now carries an outstanding balance equal to the extras. That balance is what you invoice.

Step 2: Set up your invoicing identity once

Before the first invoice goes out, set the details that appear on every invoice — you do this once.

These are stored against your store, so every invoice you issue inherits them. You're not retyping your tax ID per invoice.

Step 3: Pick the channel and issue the invoice

An invoice is delivered through a payment provider, and the provider you choose decides how the customer pays. There are three real options for most businesses (plus cash for in-person records).

Stripe: get paid online, hands-off

If you have Stripe connected, issuing a Stripe invoice creates a native hosted invoice — a Stripe-branded page with a pay button. The customer gets the link by email, pays by card, and the invoice transitions to paid on its own through Stripe's webhook. You don't mark anything manually, and the payment is recorded back against the order so your revenue stays reconciled.

This is the default to reach for: the customer added an extra, you issue a Stripe invoice for the difference, they tap pay, done.

Manual PDF: bank transfer or cash

For clients who pay by bank transfer — common in B2B — issue a bank-transfer invoice. The system renders a numbered PDF that includes your bank details (account name, bank, IBAN, SWIFT) so the customer knows exactly where to send the money, emails it to them, and stores it. A cash invoice works the same way without bank details, as a record of an in-person payment.

Shopify: keep it in your store

If you're a Shopify-connected merchant, issue the invoice through the Shopify channel and it's created against the matching Shopify order, so billing lives where the rest of your store's money does.

What happens after you hit issue

Issuing is asynchronous, and understanding the states saves confusion:

Because the invoice is built from an immutable snapshot, it always reflects what was owed at the moment you issued it. Add more add-ons next week and you issue a second invoice for the new balance; the first one stays exactly as the customer received it.