Adam Clarke on 1 Kings 9:11

Solomon gave Hiram twenty cities - It is very likely that Solomon did not give those cities to Hiram so that they should be annexed to his Tyrian dominions, but rather gave him the produce of them till the money was paid which he had advanced to Solomon for his buildings. It appears however that either Hiram did not accept them, or that having received the produce till he was paid, he then restored them to Solomon; for in the parallel place, 2Chr 8:2, it is said, The cities which Hiram had restored to Solomon, Solomon built them, and caused the children of Israel to dwell there. Some think that they were heathen cities which Solomon had conquered, and therefore had a right to give them if he pleased, as they were not any part of the land given by promise to the Israelites.