Currently I am attempting to deposit TF2 keys. However, whenever I attempt to do so, I receive the error

"Your trade offer URL is unusable. Please verify your trade offer URL and retry."

I have not changed my trade offer URL, from previous purchases/deposits that went through successfully. Furthermore, I double-checked the trade offer URL and it works completely fine. Would appreciate some help.

It probably is just a temporary Steam error if you have successfully purchases/deposits before.