Start with people who already trust you
Cold JV blasts are why people ignore "joint venture" mail. Ask three people who have an audience that matches the offer. Give them the brief and their link.
Make reporting boring
Weekly: clicks, sales, amount owed. If the script can show that, use it. If setup is heavier than the launch, track the first three by hand and install later.
Do not promise exclusivity you cannot keep
The package includes resale terms for the software itself. Your offer's partner terms are separate. Write them down. Confusion here is how JVs get ugly.