I can't reproduce your described problem (using web build). When buttons are highlighted blue that means they are selected. Can you confirm that you had 200 coins, selected tomato (highlighted blue), and tried inserting one tomato and it didn't work? Perhaps, can you play again reproducing this situation to confirm (I know it's asking a lot for you to try again)? The closest I get is having 200 coins and trying to insert a bunch of tomatoes, eventually I couldnt afford more and so the button gets disabled/unselected stopping you inserting more. With high gold income this "running out of gold" can be a brief moment. But that doesn't sound like your description, so I'm trying to understand better. Thanks for your feedback/help :)
UPDATE: I have updated it to fix the selection issue others reported, as this seems to actually be impacting the experience. If you're able to try test to see if you issue still exists that would really be appreciated. If not, no worries :)