You can't use + to concatenate strings in C, and there is no char() function. You can use + to concatenate Strings (the capital S makes a difference) but using Strings is discouraged because causes problems with MCU with small ram memories like Uno.
Try
char newMessage[BUF_SIZE] = { "FMRC Exhibition 2019 Admission : Adult \xA35.00 Child \xA33.00 Under 5's free" };
(163 is A3 in hex)