The lite version does not have a form name, because in the lite version there is only a single search form, it is not possible to create multiple search bars with it.
Multiple search bars are supported in this Pro version, and because of that a search form name is required. I see you have made an imported search bar already. You can access the settings here: https://i.imgur.com/rnFSTNA.png
Don’t forget to disable Ajax Search Lite – it is best to have only one version active as they share some resources.