Most things here are handled by your own workspace administrator, who can change access and send invitations. Anything they cannot fix comes to EPX IT.
Use the sign-in button on the front page rather than an old bookmark, and sign in with the email address your invitation was sent to. If you are asked to set up multi-factor authentication, that is expected: the portal requires it. If sign-in still fails, your account may have been deactivated, in which case your workspace administrator can reactivate it.
Invitation links expire, and they are also replaced whenever an administrator sends the invitation again, which makes the earlier link stop working. Check that you are opening the most recent email, then ask your workspace administrator to send a fresh invitation. If you have already accepted the invitation, sign in instead.
Send us that reference. It is the only thing that ties what you saw to the record of it on the server, so quoting it turns a report we cannot investigate into one we can. Tell us what you were doing at the time as well, and whether the thing you were doing took effect.
Your own workspace administrator does this from Settings, then Users. They can invite a new person, change what an existing person can see, and deactivate someone who has left. EPX IT does not make these changes on your behalf without your administrator asking.
Two different things produce that. Either your role in the workspace does not include it, which your workspace administrator can change, or it belongs to a part of the product your organisation is not on, which we can talk to you about. If you are not sure which, contact us and say which page it was.
Email support@epx.co.uk. Tell us your organisation and, if you have one, the reference from the error you saw.