Voucher Number on the invoice!

 Hi Expert,

      as we know, the document sequence in payables will be shown as voucher number on the invoice,

 when we entry  and save the AP invoice manually,the voucher number will generate automatically,now we use two process:

1,Create DM from RTS transaction,i know that system use standard API to create DM.After DM is created,i found that no voucher on the invoice,.

2.Intercompany invoice.but for these two process, we use request to import the intercompany ap invoice ,after the request is finished.,i found that no voucher on the invoice

 So ,why there is no voucher number on the invoice?it  is just for manual entry source?