Thanks for your question.
First, try pairing the Forerunner with a different phone - if it pairs ok, this confirms that the Forerunner is working correctly.
Try force-closing all other apps on the phone in case they are causing a conflict. Un-pair the Forerunner from the phone, shut down the phone, restart it and try pairing the Forerunner again.
Let me know if that works or if you need further assistance...