Thanks for joining us here today, @LauraF11.

I know a way how you can add letters to your invoice number. You can add a header to your invoice template, so you can manually enter the invoice number with letters. Let me walk you through how.

1. Go to Customers. Then, choose Create Invoice.
2. In the invoice page, tap the Formatting tab and then Customize Data Layout.
3. Scroll down and select Basic Customization.
4. In the Header tab, look for Other and then mark for Screen and Print. Enter a name in the field.
5. Click OK. See the attached images below.

With the above steps, you're able to keep track of your invoices that begins with letters.

Feel free to check out this link to help you manage customer-related tasks: Topics about your company's income and customers.

Still have questions? Click the Reply button below and I'm more than willing to answer them for you. Take care and have a wonderful day ahead.