The captcha on the quest are messing up. I will type the word in the captcha and it keeps telling me the word is wrong. It has been happening to me the past couple of day.
Do you have multiple tabs open, by chance? You have to click the captcha first in that case, on the first tab you opened. Only the most recent one will actually go through.
I think this only happens when you click to buy two different things in the main shops without completing the transaction. This has been happening to me when I click the search shops links on quests and end up with the captcha screen in two tabs. The captcha code doesn't seem to be specific to each item/page. So the most recent code is the correct code -- I'm not sure if you can type the new code in the first captcha tab, but you should be able to buy normally from the second/most recent captcha page.
I have had it happen a couple of times. I would have to get one Item on a quest and the captcha would tell me I am wrong on it. But it not as bad.
When this happens, do you by chance have an item purchasing open in another tab?