Error 429 deals with exceeding daily, secondly or minutely requests limits:

Rate Limited Second - If your requests exceed the per-second rate-limits
Rate Limited Minute - If your requests exceed the per-minute rate-limits set on your account
Rate Limited Day - If your requests exceed the per-day rate-limits set on your account

If you're seeing this often, please reach out to us at hello@locationiq.com with your requirement and we'll suggest a suitable plan.