We had an accepted manuscript and we are collaborating with one institution in South Africa. When the South African institution received the invoice for the manuscript, the pronounced that they would pay for only their staff 3/5 of the cost. Now we have requested the journal to split the invoice such that 2/5 of the bill is charged to our institute and the other 3/5 to the South African institute. My question is is this ethical or legal to split an invoice?