Customer Invoice number

Hi,

I am trying to implement Lockbox. I need to create an BAI2 file, which consists of "Customer Invoice". I need to know where can we get the Customer Invoice number. We can post Customer Invoice using FB70, after giving all the information, I got a message "Document 1051 was posted". Is 1051 the Customer Invoice number ?

I Will award points surely.

Thanks

Rajanikanth