There are many ways to market your optin. You can make mock ups and share on social media, make pinterest pins, create videos of the product in Canva to share on YouTube, Tik Tok or Instagram. 

Write an article with links and submit to Medium, add a link to your LinkedIn profile. Share on your Facebook page and in groups that allow promotion.

What about a freebie swap? Promote a freebie from a friend on your platforms in exchange for their promotion of your lead magnet.

Create an affiliate page for products and add the lead magnet as a product to capture affiliate cookies. Add an upsell so visitors will see options for additional products.

Look at the cookie settings for these products and set long term cookies so affiliates can benefit. .

And if you do not have any upsell, let your affiliates know about other products that may be similar to your optin that they can promote. 

In emails affiliates could promote the paid product and add “Want to check out XYZ’s free product before your buy?” then include the link.