Pay On Receipt AutoInvoice Request need to generate the voucher number

We want to implement Auto AP invoicing process for that we have changed the following :

Purchasing  --> Self Billing Tab

and Selected Pay On = Reciept  

Now we executed Pay On Receipt AutoInvoice.

Invoice gets generated but :

1.the voucher does'nt gets generated.

2. the Document category name is set to Standard invoice , We need as per our requirement

What are the setup changes required for the same

Thanks

Rupali