Check the yellow lights on the start and finish gates are blinking slowly and at the same time.
if they are not, you need to:
Replace the batteries on both Gray boxes with new ones (this is important, as the gates will not pair if the batteries are not 100%) Do not use rechargeable batteries, only Alkaline.
Make sure your ArenaGear timer is on a 2-gate mode. Check the settings while connected to the Start gate (“MASTER” should show on the app banner)
Pair the S and F gates as shown on this video: https://youtube.com/shorts/_FNVYZTURMU?feature=share (Remember to turn off all black boxes prior to doing the pairing)
If you have more than one set of gates, you may have accidentally paired the F gate to some other S gate, follow the pairing procedure in the prior step