Open any default DP file to see how it's done. I copied this from the instructions with one of Martin Wright's CFS2 weapons packages. I'm sure the principle is the same for CFS1.
Payloads will only function correctly if the Aircraft Dp file contains appropriate "dummy" gunstations and guns for the given weapon type
gunstation.4=
2,-1,4,0.00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ;
Rocketsgunstation.5=
3
,21,8,0.00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 ;
Bombs
Each gunstation will have a corresponding gun.x entry further down the dp.
The values in this entry set the maximum of a particular weapon type that can be carried.
Often the "Bomb" gunstation will have a gun setting like:
[Guns.5]
gun.0=
3
,0,0,0,0,0,0,0
and this means that the aircraft will not carry more than
3
bombs. This number can safely be altered to a number greater than the maximum number of bombs you will ever put in a payload.