If you need to create and manage Tenders invitations, you’ll need to be given Tender Administration permissions.
Your Org Admin can do this. They will follow the instructions here.
Why can't I see the Tenders button?
The Tenders module is not available on all projects. Contact your Org Admin if you need access. Or, if you are using Aconex for a project based in America, you'll see Bids instead of Tenders.