What happened
A complete-looking trade URL can still identify the wrong recipient. The partner parameter represents account identity; a familiar avatar, copied nickname, or correct-looking token does not make another account yours. Ownership validation and live link availability answer different questions. Resolve an account mismatch before asking whether the token works, otherwise even a functioning link may point somewhere you did not intend.
What to check
Sign into the Steam account you use to enter CASECS2. Open trade settings from that same session and copy its own address. Avoid links supplied by friends, trading accounts, or old shared profiles. Save the full address without editing its numeric parameters by hand. If ownership validation refuses it, return to the account context and check which profile is actually active in each browser.
Worked example
Imagine two personal accounts with identical display names. Your phone uses the first, while the desktop browser uses the second. You copy a link on the desktop and paste it into a website session belonging to the first account. The name looks right, yet the ownership error is useful evidence. Replacing the nickname will not repair the mismatch; obtain the link from the correct account instead.
Result and next step
A resolved case has matching authenticated ownership and saved recipient, followed by a separate current link check. Tell support whether you switched accounts, and provide the public ownership error. Keep the full URL private. Do not splice another partner number into an existing token or request a bypass. Read Steam trading information and CASECS2 account guidance to distinguish recipient identity from delivery status.