@IniNaadiJ 

1. why would you need more than one internal customer for a site? The internal customer represents the site itself, so it will always be a 1:1 connection. A common confusion is that the internal customer is the site with which the original site can do business with, but that’s not the case.
2. Supplier Invoice will be created automatically in the demand site once the customer invoice is Printed in the supply site → a new record will be created in External Supplier Invoices in demand site/company

@IniNaadiJ
Is it that your company can behave as different customers/suppliers in internal trade?
If you are not dealing with a live data setup yet, I wonder if you can consider defining multiple sites for the company which behaves as each customer/supplier situationally. Then you will have one to many connection. This will help you to define configs and defaults too. Most importantly the addresses. 

Also, you can choose to change the internal customer, supplier connection from the site at any time you want. For you to consider a customization here, what you should first think is what conditions make a supplier/customer selection the internal trade. Based on that, I guess you can think of a logic to make a stakeholder selection in the internal trade. 

Dear Marcel,

I have done the testing and I could not get the supplier invoice automatically.

Please let me know what I have missed

• Raise PO> Release> Send PO

• Message defaults > Set the INVOIC  (This is for the automating invoice)

• Go to incoming Customer order

• Register Arrival

• GRN & Complete

• Raise the Customer order & Deliver and raise Invoice

• Invoice will be generated

• Send Invoice (Ideally supplier invoice should be generated but this command is inactive)

Regards

Naadira

@IniNaadiJ See if you have added INVOIC message class in the customer Message Defaults. Also to complete the fully flow, make sure you have SUPEXT message class in Supplier > Invoice > Message Defaults as well.  

Dear Vimukthi,

Thanks for the reply,

The following basic data were set as you mentioned. But still external supplier invoice unable to get.(Upto customer invoice generation inter-site process works fine)

In the customer invoice> Send invoice command is inactive.

Any advice on that.

Regards

Naadira

@IniNaadiJ 

Prerequisites (non-Einvoice)
>A customer invoice with Preliminary status must exist.
>The Method Default check box must be selected in the Customer/Message Setup tab for a row with the message class INVOIC.

Dear Vimukthi,

Thanks I was able to generate the Invoice and do the send invoice option.

But from the supplier side automatically external supplier invoice is not generated.

Can you please explain what I have missed here

After sending the invoice still unable to auto generate the external supplier invoice

@IniNaadiJ 
I found some steps I have made in a previous topic

Pls check this. 

For the documentation from your environment use /Invoic/tbwExternalIncInvoiceHead.htm after documentation URL or take F1 for the window ‘multi-company external supplier invoices’