OCTETx is a String (capital S). msg is a character array.
You're advised to stay away from String in favour of c-strings but I think that below will solve one error
String msg[8] = {OCTET1, OCTET2, OCTET3, OCTET4, OCTET5, OCTET6, OCTET7, OCTET8};
Please post your full code (and notice how I posted code using cide tags).