How to Negotiate for a Newsletter

I wanted to sell sponsored posts as something like an entrance to a longer partnership. Most companies who starts with a sponsored post on social eventually become newsletter advertisers. Sponsored posts are a low stakes way to explore if this is a good fit, if we work well together. So I'm very lucky that many of these letters are often booked out months in advance. Matter of fact, an advertiser about a year ago, they bought six months of all the newsletter ads and they would have bought 12 months if I had let them.