How the Invoice will split

Hi all,

On What Basis Invoice will split in SD...

what are the basic considerations to take for the split. in header( vbrk) level and also item level (vbrp).

Here Invoice is Spliting for what basis we don't Know .....

the fields and values are every thing is correct here and also we checked ..

here we saw only the billing date is different but in some invoices are not spliting even though the billing date is different...

thanks for all