I am using WP Gridbuilder for sorting and facet filters. I have stored the DateTime field as a timestamp in a custom database. If I use the sorting filter using the timestamp value. It doesn't recognize it. I have contacted them. They replied that the custom field is not associated with the post.
However, the data is associated with posts. I have checked the same data stored in the post_meta table where the sorting option is working. If I store the value in a custom table, it won't function.
I don't know how to find the solution for this.