Seq numbering is not generated for chargebacks generated from Trade management

Hi,
I am trying to create chargebacks from trade management and document seq number is not generated for those transactions:


1) Enable the Sequential Numbering Profile Option
2) Enable the AR: Document Number Generation Level Profile Option
3) assign chargeback transaction type in system parameters
4) Define Sequences
5) Define Categories
6) Assign Sequences to Categories


please help,

Thanks,

Ouafaa