How to hide stripe secret key using lambda function

[fool]

I think you probably would benefit from reading this article:

[Support Guide] Using environment variables on Netlify correctly

Last reviewed: August 2023 The preferred way to use environment variables in Netlify is to set them in our environment - be that in the Environment Variables settings UI (on the site’s “Build & Deploy settings” page), or via netlify.toml. You’ll want to choose the right pattern to meet your needs. Setting variables in our UI may be considered a bit more secure, since only people with access to the Netlify admin UI for your site can see them, rather than “anyone who can clone your repo!”. Thes…

So, my answer would be the same as @talves around making sure you access it as suggested.

Do note that functions do NOT use the variables mentioned in netlify.toml, only the ones shown in our UI.