This is shown as a type error, however it is a valid API call:
// returns matching product results
const productResponse = await swell.products.list({
id: { $in: productIds } // productIds is an array of IDs
})

And trying to do this same thing with the "where" flag actually doesn't properly return any products.
// this doesn't work even though it seems like it should (returns no results)
const productResponse = await swell.products.list({
where: { id: { $in: productIds } }
})