cc2640R2F error: 0x3E: Connection Failed To Be Established

A "Failed to Establish" (0x3E) error occurs if the master is unable to receive a packet from the slave within the first 6 connection events after sending a connection request. This could be caused a number of reasons. Here are a few possibilities:

1、The RF performance on one or both devices is not good, so the slave either never receives the connection request, or the master never receives any packets from the slave during the first 6 connection events. The RF Performance could be bad due to a failed CRC, collision or maybe the devices are just out of range.
2、There could be a timing issue in either device. If the link layer clock on either device is not running at 32.768kHz (within the tolerance set using the HCI_Ext_SetSCACmd function; default is +/-50ppm) then the timing will be off and the slave might not be listening at the correct time to receive the master's packets.
3、If the slave device is advertising with the whitelist filter policy set to GAP_FILTER_POLICY_WHITE_CONor GAP_FILTER_POLICY_WHITE then the slave will ignore the connection from the master and continue advertising normally, and the master will get the 0x3E error since it does not receive any packets from the slave during the first 6 connection events.