Invoice Number = Order number

Hello Valentin!
Apologies for the late response, I was on a short holiday and because this forum is for the free version I gave priority for email support. If you have any additional questions, please email us directly at [email protected] with your order number or license key(s), as a paying customer you are entitled to priority support!

I would not recommend this, please read this first: Why is the PDF invoice number different from the woocommerce order number?

If you still want them to match after reading this, scroll down on that page for a solution:
https://docs.wpovernight.com/woocommerce-pdf-invoices-packing-slips/invoice-numbers-explained/#but-i-want-the-invoice-to-have-the-same-number-as-the-order

Hope that helps!
Ewout