You may have been notified of an invitation to a new project on GoContractor. In some cases, this is by an Invitation code.
Your supervisor or GoContractor administrator has created a unique code to invite you to GoContractor with. They should have provided you with this code in some way.
If not, you will need to reach back out to them to provide you with this code. GoContractor does not provide invitation codes as this must come from an administrator.