AFAS uses different terminology than Zenvoices for these fields:
The Zenvoices field invoice number is called document number or creditor invoice number in AFAS.
The Zenvoices field document number is called invoice number in AFAS.
However, it is possible to deviate from this via the administration settings (Manage / Environment / Administrations, tab AFAS for the relevant administration). The following options are available there:
Copy the invoice number of purchase invoices to the invoice number field in AFAS: enable this option to fill not only the AFAS document number but also the AFAS invoice number field of purchase invoices with the invoice number from Zenvoices. If this option is disabled, AFAS will determine the invoice number itself.
Copy the invoice number of sales invoices to the document number field in AFAS: enable this option to fill the document number field of sales bookings in AFAS with the invoice number from Zenvoices. If this option is enabled, the invoice number field in AFAS will not be filled and auto-numbering must be enabled for this field in AFAS.
More information about AFAS booking fields can be found in the AFAS knowledge base.