Admin > Accounting > Auto Numbers > Select Sale/Purchase Type
The administration of Auto numbers allows you to set (or re-set) the sequence of the numbers for invoices etc. Very useful when transferring from another system to Actionstep.
The ability to "Mask" a number is done here too you may want to start your invoice sequences on an annual basis so you would be able to put the year as the mask, reset the number back to 1 and start again for the year.
Masking can be used to add any other information within your invoice number. Just put the extra information before or after the X and it will appear as part of the invoice #.