Open the Bluetooth® setting menu of your smartphone and remove the module record before you try again.
Connect with the smart device and bond with it to store security keys on both ends.
Factory reset your module to remove the security key from the module.
Once reconnected with the smartphone, it may still think you have the key (but your module does not have it). It will generate a security error and disconnect. To resolve this, just delete the record of the module from the smartphone to completely remove the security key.