What does 2 Chronicles 21:3 mean?

Their father gave them lots of gifts—silver, gold, and valuables—plus some fortified towns in Judah. But he made Jehoram king, because he was the oldest. 2 Chronicles 21:3 - Modern Text Bible

(Jehoshaphat provided for all his sons, but gave the throne to Jehoram as the firstborn, following the custom of primogeniture.)