Two people, one room. Talk on the record, keep private notes, and make a sealed offer: each side enters its real limit in private, and the room only says whether a deal exists.
You got a link and a passphrase from the other side. Enter both.
Give it a title and a passphrase. Facts from the letter reader come with you.
Send them the link from your own email, and a separate guest passphrase by another channel. No account needed.
Talk on the record with a tone check in the middle. When you're ready, both enter a sealed limit. The room says deal / close / no — never the numbers.
Everything in Talk is visible to both sides. Messages are timestamped and can't be edited or deleted — that's the point.
Enter the most you would pay (or the least you would accept). The other side does the same. The server compares the two and tells you both only one thing: whether a deal exists. Your number is never shown.
What the letter (or the claim) says. Both sides see this.
Your bottom line, your weak spots, what you'd trade. Never leaves this browser and is never posted.
Tip: writing down the weaknesses of your own position before negotiating raises settlement rates in experiments (Babcock & Loewenstein).
Set a guest passphrase. Send them the link by email and the passphrase by another channel (text, phone).
Send the passphrase separately. Anyone with both can read Talk and enter a sealed limit as the other side.