The synchronize symbol option isn't available for graphic symbol?

I have recently learned that I can use “synchronize symbols” instead of manually entering the start frame for every keyframe of a symbol on a timeline which saves me alot of time, but I can’t seem to get it to work for a symbol on my main timeline. I have set the symbol to loop for every keyframe but the “synchronize symbol” option is whited out. I’m not sure what I’m doing wrong? I made sure the symbol has the same number of frames as the main timeline, I’ve made sure there aren’t any other symbols hidden in the same layer but can’t get the option to present itself? Any ideas on what I might be doing wrong?