Thank you for your query, Yoona Cho.
Do you perhaps have more than one Amara account? If yes, make sure you are logged in the one for the pro job requests, then try the link again. The message you mention also appears when you are not correctly logged in when you open a link for these private subtitling jobs.
If you are correctly logged in, please ask again in a ticket. Please mention "OnDemand" in the title of the ticket, as this will accelerate its processing by Amara's tech staff, who will be able to answer you.