You can change the filename for your invoices from the Templates section by following the simple steps below.

Step 1: Open Simple Invoice from your Shopify store’s “Apps” section.

Step 2: Click on the “Templates” on the Simple Invoice dashboard.

Step 3: Click on the Other Settings section, and change the filename from the Document Filename field.

By default, your document filename is invoice-{{ order.name }} which is shown as invoice -#1001 when it is sent.

If you want to use your custom invoice number as a filename, you need to change the {{ order.name }} variable to {{ order.custom_invoice_name }}.

Step 4: Click on the Save button.