Translation:The merchants can hand over the money to us.
In this sentence, "nobis" is an indirect object, which takes the dative case. In English, a similar sentence would be: "The merchants handed us the money." Without the preposition, "us" clearly functions as the indirect obkect of the verb "handed" -- rather than simply the object of a preposition. Latin does not use a preposition for this purpose. The meaning is completely coneyed by use of the dative case.