The IOS version is actually 15.5 but there wasn't a selection for that in the list.

Dear Kootom Thank you for contacting FOBO and we are sorry for any inconvenience caused, Unfortunately we regularly see new batteries that are dead in packets or discharge quickly as soon as used. Before we do a replacement for sensor, we strongly recommended to change the sensor battery to a new battery and check the sensor's battery voltage with an ohmmeter if it is available and it should be more than 3v for the new battery. Kindly ensure for sensor's battery first and then do the below troubleshooting steps: 1. Logout and uninstall FOBO Bike 2 App from your iPhone. 2. Download and Reinstall FOBO Bike2 App from App Store and Login with your email again, 3. Accept and allow all App permissions , specially Bluetooth and Allow as always for location service. 4. Take out the sensor battery wait for 15 seconds and place it back. 5. Ensure valve is clean without any dust around the valve's pin. 6. Install sensors one by one by press and hold on sensor’s box then selecting “Install” and continue through App instruction to complete instalation. 7. Please ensure there is a hissing sound while screwing sensor onto the valves. 8. Please ensure that there is a minimum of 5 thread count on the tire valve for the sensor unit to be screwed on. If there is insufficient thread for the tire sensor, it may lead to air leakage. 9. Try sensor install on other tire Bike/Cars valves , this is to ensure that this issue is not related to tire valve, Please let us know how it goes, if you have any issue arise, you may revert to us for further assistance with writing to FOBO@SALUTICA.COM.MY Best Regards Amir Bayati FOBO Support Team

Amir, Thanks for the quick response! I checked the batteries that are in the sensors wth my Ohm meter already and they show a bit higher than 3v so they are not discharged. There was a hissing sound as I screwed it on the bike. I did remove the battery for 15 seconds and reinstall. No joy. I'll go count the threads but I believe there are 5 but I'll verify that with the lock nut in place. I've done everything you suggested and I still cannot get the sensor to pair with the iPhone app. I've tried pairing with it on the bike, off the bike and on another vehicle. Nothing works. I just bought them from Amazon, should I just return them?