You can create as many number sequences as you like to name invoices, credit notes and dunning notices as required. To do this, go to "Settings > Documents > Sequences" and click on "Generate Sequence".
Then set all the settings for your new sequence as required.
Finally, save your number sequence. The overview now shows all created number ranges and their last assigned output.
Now select the sequence in the desired template. For invoices, go to "Settings > Documents > Invoices" and select the sequence for invoices.
From now on, the sequences are automatically used as invoice numbers in invoices. Please note that the sequence for invoices and credit notes must not be identical, otherwise conflicts may arise. For example, you can use prefixes such as "R" and "G" to distinguish the number ranges for invoices and credit notes.