Means that your scheme "start -> byte1-byte2-byte3-byte4-byte5-byte6-byte7-byte8-stop" is nonsense. Each UART byte involves a start and stop bit. Standard UARTs are fixed to 10 bit frame with 8 bit payload, start and stop bits are mandatory to perform the bit synchronization. No way to send the start bit only with first byte.
There are different options to send multi-byte packets that can be unequivocally decoded by the receiver. Beside usage of unique start (or possibly) stop characters, the start of a packet can be indicated by a preceding idle period as in MODBUS RTU protocol.