Im getting "Makefile:7: *** missing separator. Stop." when im trying to use "make"

Question

Im following a tutorial series and ive wrote this Makefile but im gettings this error

Makefile:7: *** missing separator.  Stop.

This is my Makefile:

ASM:nasm

SRC_DIR=src
BUILD_DIR=build

$(BUILD_DIR)/main_floppy.img: $(BUILD_DIR)/main.bin 
    cp $(BUILD_DIR)/main.bi $(BUILD_DIR)/main_floppy    
    truncate -s 144k $(BUILD_DIR)/main_floppy.img
    
$(ASM)/main.bin: $(SRC_DIR)/main.asm
    $(ASM) $(SRC_DIR)/main.asm -f bin -o $(BUILD_DIR)/main.bin