How did God cover the shortage when the Jerusalem common kitty ran out?
God covered the shortage by having Paul take collections for the poor saints in Jerusalem wherever Paul went. When the Jerusalem common kitty ran out and new believers were not filling it fast enough, those collections supplied the need.
Les explains that the Jerusalem church was a called-out group of Jewish believers, not the church as we understand it, and they lived out of one common kitty. That fund would run out unless new believers kept adding to it. It did run out, and God in His grace and goodness covered the shortage through the collections Paul took wherever he went for the poor saints in Jerusalem.