Error when search blank page

Hello i use this plugin to create a search field for mywebsite where i’ve crate five CPT and a lot of custom post type with ACF.

I need to create two different search module. One of this i like to search the singe post for one custom post field. So in plugin i’ve setting:

> Data Type: Custom Field
> Data Field: name of custom field (evento)
> Widget: DropDown
> Compare: Equals
< Widget Config: Drop Down Option : blank

If i try to search on front end i have a blank page without any result. Why? Where wrong? Thanks much

https://wordpress.org/plugins/wp-custom-fields-search/