There are a number of things we know that are according to His will. There are a number of things we know that are not according to His will. However, there are a great number of things which we do not know the will of God until He reveals them to us. God reveals them to us most of the time through events in our life. The Lord gave Paul an answer to his prayer in 14 words.
All prayer is answered.
God either says YES or NO . Sometimes the YES is not always as we expect or want it. Denial of Paul's request did not mean destitution but deliverance. The weight was not lifted but greater strength was given to bear it. Paul was given something better than he asked for .