The negotiation is between the RFP Point of Contact (POC) and the Vendor POC. Essentially, you will be rejecting the response back to the specific Vendor for their individual response re-submission.
Once the responses are viewable by you (responses are submitted), you can initiate a Negotiation. For example, if you need more information you can request it.
In the example below, the initial response was less than stellar. So let's kick this back for a re-do. So initially I scored this response as a 1 out of 5 and made an internal note of my analysis.
You can click on the Negotiations tab and start a Negotiation. This kicks off a message to the Vendor POC. The body of the message contains your text.
The Vendor POC receives the message and the link takes them directly into the Proposal. The Section is highlighted for visibility.
The individual Question is marked with the info-icon. This response is Rejected on their side, so it initiates a task for their completion.
Once they mark the response as completed/approved, you will see the updated response on your side.
Back on your side, you can see the updated responses from that specific Vendor.
Now I like this answer better, so I update my score and my internal note.