When users click the link to sign the document, they are redirected to the Adobe Sign account Login page. But they are not able to log in or sign the document.
INACTIVE users are not allowed to sign the document. Adobe Sign directs them to log in to their Adobe Sign account, where they are restricted to log in.
Contact Adobe Sign support https://helpx.adobe.com/contact.html. Make sure to log in using the Adobe ID. Support agent can help the users to ACTIVATE the account, which enables them to sign the document.
Choose Adobe Sign as product to get in touch with Adobe Sign support Team.