Depending on the region, the time limit to respond to a booking request or invitation to book is 24 or 48 hours.
Once the time limit passes, the booking request or invitation to book expires. You are then free to send another booking request to the advertiser.
If your booking request hasn't been accepted, you can try contacting the advertiser again to understand why they might not have accepted you.
You can also send booking multiple booking requests to advertisers without worrying about being charged twice; once a request has been accepted, the others will automatically be canceled.
Questions? Let us know, we're here to help!