By clicking the Test link associated with a channel destination, you are effectively testing the user credentials provided by a wholesaler/distributor. At times these third-parties may change the destination setup. It is the publisher's responsibility to inform TitleLeaf of changes to said setup. Failed distributions with a message of upload failed are an indication that the destination is not properly configured. If the channel destination remains inaccessible for multiple days, contact the third party.
After clicking the Test link, you should either see an accessible or inaccessible response.