Why have I not received the 1,000 V-Bucks for the Battle Pass after subscribing to the Fortnite Crew?

You will only receive the 1,000 V-Bucks if you purchase the pass and then subscribe to Fortnite Crew within 14 days (the pass must be active at the time of subscription; if a new season starts, you will receive the current pass instead). Note that if you get the V-Bucks back after subscribing, your pass will convert to requiring an active subscription to unlock premium rewards.

If you buy a pass and subscribe to Fortnite Crew more than 14 days after purchasing the pass, you will not receive your V-Bucks back but your pass will not require an active subscription to unlock premium rewards.