In Fortnite, if you purchase the Battle Pass, you will unlock access to various rewards, including skins, V-Bucks, and other cosmetics, as you level up your Battle Pass. However, the rewards you receive are typically tied to your Battle Pass level and not your overall player level (like level 45 in your case).
When you buy a Battle Pass, you will not automatically receive all the rewards instantly. You will need to level up the Battle Pass by earning XP through gameplay, completing challenges, and participating in events. The Battle Pass generally has multiple tiers, and you'll need to progress through those tiers to unlock the rewards.
While being a higher player level may give you some advantages in gameplay, you will still need to put in the time to earn XP and level up your Battle Pass to unlock the rewards associated with it. If you want to maximize your rewards without too much grinding, focus on completing daily and weekly challenges, as they often provide substantial XP boosts.