The problem is the ”'s in your formula. You’re using curly quotes. Airtable only recognizes straight quotes which look like this ". Replace the curly quotes with straight ones and your formula works, your nesting is perfectly fine as is.
Got it! Thanks so much! Here is the final working formula in case someone needs it. I actually had to go in and pick the functions out of the list. For some reason copy and paste isn’t great for making functions.
You could make this a little more compact by using SWITCH instead. I recently did something similar where I needed to convert from the numeric value returned by MONTHS into the abbreviated month name. Here’s how I’d structure it in your case for the weekdays: