If you are using our Order Printer Templates with the Shopify Order Printer app, you must be aware that it does not support sequential invoice numbers by default.
However, it is possible to do so with a slight change to the template code. The way to do it would be to find this code in your template:
{{ order_name }}
And replace it with:
#{{ order_number | minus: xxxx }}
Note: You must replace the xxxx in the above code with the correct number to start your sequence.
The order number starts at 1 for your first Shopify order, so you need to subtract the required number to get your correct series.