against (prep.)
This meaning of against is quite old: the OED's first citation is c1225.
In exchange for, in return for; as an equivalent or set-off for; in
lieu of, instead of.
1957 H. Roosenburg Walls came tumbling Down 19 We were intended
as exchanges against some high-ranking Nazis.
1997 D. Mernagh-Ward & J. Cartwright Good Pract. in Salon Managem.
v. 106 A voucher redeemable against services during a quiet period
of the year may be offered. (OED)
In exchange for
a lower rate against the dollar m-w
... but where there is a promise against a promise, one promise is
the consideration of the other, because each may have his action
against the other for non-performance. The English Reports: King's
Bench (1888)
Payment system. Most oriental carpet import transactions are paid for by cash either
against receipt of the bill of lading or on arrival of the carpet lot.
Markets for Oriental Carpets, vol. 1 (1969)
The 1976 Act laid down procedures for the release of bonded labourers
and specified that no labour could be promised in lieu of payment of
debt and correspondingly no advances could be given against a
promise of labour. Anti-Slavery International; Enslaved Peoples in
the 1990s (1997)
The petitioner addressed a letter to Livingstone directing that the
Treasury notes be delivered to Seaboard against payment by that
company of $9,914,212.71. Report of the Tax Court of the US
(1959)