Modelling Capacity Restriction in F&R

Hi, I am attempting to model the following scenario in F&R. However, I do not have the exact know-how of how to do it. Can someone please throw some light on the same.

SCENARIO DESCRIPTION

My supply network has 2 vendors supplying to a DC & Store. Let's say one of my preferred vendors can only supply 500 units of a particular product (production quantity restriction).

Now, after having executed a forecast, I get an OP for the said product and vendor for quantity 1000 units.

How do I model this constraint so that the system only plans for a maximum of 500 units and the balance 500 units of requirement are automatically passed on to the other vendor or the DC, depending on the availability?