Was playing around with tellraw and trying to get an rpg-like interface done, but it always said "Invalid json: Expected at at line 1 column _". So I played around with it some more, and discovered that when you use a tellraw command within a tellraw command it only accepts one word. Example:

/tellraw @p {"text":"Museum: Are you sure you want to visit the museum? ","extra":[{"text":" Yes ","color":"green","clickEvent":{"action":"run_command","value":"/tp ~ ~ ~"},"hoverEvent":{"action":"show_text","value":"You will be instantly transported to the museum"}},{"text":" No","color":"red","clickEvent":{"action":"run_command","value":"/tellraw @p Nevermind, then"},"hoverEvent":{"action":"show_text","value":"You will stay right where you are"}}]}

Paste that into a command block, power it, and click "No". Should give you an error message. Then try it again, replacing the "Nevermind, then" with "Okay" or something. Should work fine.

(P.S. I apologize if this is a duplicate, I really did try searching