I checked under preferences and under some tabs on the website, but i just cant seem to find out where the box is for me to input my trade URL. This problem just started occurring today because its telling me my url is invalid even though i am still using the same one and i have used this site many times in the past.

Im getting frustrated because i want to buy a game but the site is telling me invalid URL

FIXED
(its under the personal item shop page)