How to communicate with YouTubers?

Hey Hackers!

I am building a note-taking tool and I have launched it on Product Hunt, which gave me a lot of traffic.

But after that, I thought of nothing to promote it but to write cold emails to YouTubers in order to get my app reviewed.

Luckily, I got several replies from YouTubers with tens of thousands of fans. They asked me to sponsor videos.

I mainly have two problems in replying to them.

1. How can I communicate with them I could only provide the Promotion Code right now to them right now without hurting our connections? (I mean maybe when the traffic is larger I would consider sponsoring with money but right now I can't)

2. How can I tell them I am comparing a few YouTubers to find the most suitable for me?

I wonder if you have ever been in the same situation. Thank you for your help in advance.