Firstly, 0xAA is a single u8 byte (in binary it would be 1010 1010, i.e. 8 bits which is one u8). 0xAA is just a number (170), and is no different from any other number.
Are you successfully subscribing to the FCM using the adl_fcmSubscribe function before trying to send the data?
Is the receiver set to the correct baud rate to receive the packet?
Are you using « 7 bits » mode on a v24 serial link?