problem during multiple vendors maintained in PO conditions (FRC1)

Dear gurus,

in this case we made a PO with FRC1 condition 3 times as 3 transport vendors.(is this corect ???)

and if not how to go further,

or if it is correct then,while doing invoice (MIRO) the restriction made on quantity OMR6 is not allowing.

the message is as follows:the invoiced quantity greater than GR quantity.

plz suggest

Bhanu