What happened
A copied trade URL may lose its ending while retaining a convincing account identifier. For the full-address form, the presence of partner alone is not enough: check whether token survived copying. This is a format problem before it is a Steam availability problem. A server cannot meaningfully verify the intended complete recipient if the input no longer contains the information you meant to submit.
What to check
Return to your own trade-offer settings in Steam and copy the source address directly. Paste into the private profile field, inspect the parameter names, and compare the ending with the source. Avoid typing an invented token or borrowing one from another account. Save the complete value, reload the page to confirm persistence, and only then ask for the separate live check.
Worked example
For example, a message displays the beginning of a long address followed by an ellipsis. You select the visible preview text, rather than copying the actual hyperlink. The pasted value contains dots and no token. Another common mistake is copying only the text before an ampersand. Both cases are repaired by returning to the original account settings, not by changing the account number.
Result and next step
Completion means the intended full URL is saved and format errors are gone; it does not automatically mean Steam accepted a live check. If the checker remains unavailable, retain that status honestly. Support initially needs the validation message and copying method, not your exposed token. Consult Steam trade information and CASECS2 guidance. Keep recipient data inside signed-in settings rather than publishing it in comments.