From the top navigation menu, select Brands → Find Campaigns.
Select the Invited tab.
Hover over the campaign and select View Proposal.
Review the campaign's proposal and select Apply.
If a brand allows negotiation, select Negotiate in the bottom-right corner of the modal, enter your proposed rates and tasks, and select Send.
Once the negotiation process starts, the application moves into the Negotiation tab and you can continue countering until an agreement is reached.