Since the MAX13488 uses a 5V supply voltage, the lowest voltage of the logic-high is higher than 3.5V. Such voltage exceeds the supply voltage of the Bluetooth module. If the Bluetooth module cannot withstand the 5V logic input levels and may be damaged, you can add a resistor in series between the receiver output (RO) of the MAX13488 and the input of the Bluetooth module to limit the output current of RO.