In Steam latest service update, Valve has decided to add a security procedure more to this series of exchanges in Steam, designed to combat malware and bots of their market: the famous, and annoying, Captcha codes.
Seen from a business point of view, it may be an issue that affects the proper functioning of the Market Exchange. Therefore, Steam has announced that they have just added a Captcha system to transactions of the market.
The implementation of Captcha has caused problems, and there are many users who have shown that affected each and every one of their previous transactions. It remains to be seen if due to these problems, the Steam withdrawn or is merely a temporary error due to the implementation of a new security system on the platform.