Yes, when creating an invoice you can always indicate the number of invoice issued in the dedicated space, even if you cannot put a number lower than the one indicated in the first invoice sent via Finom. Let's see how it works.
When creating a new invoice, you shall fill a section on the right side of the document asking you to provide the details of number of invoice, issue date, due date and payment method. Here you can chose the number or alphanumerical code you whish to put
Be aware that the system will save the number of invoices sent and wouldn't allow you to reduce this number. For example, if your first invoice will start with "3", you will not be able to send a new invoice with "1" or "2" and the system will outline you that you already have an invoice with that number.
This way you will always be able to keep the number of your invoices in order without the risk of making any mistakes.
Try it, and tell us your experience!