For range searches, Elastic supports searches for ranges with one end bound, like "pubdate greater than or equal to 2020." Except the phrasing for that would be "pubdate:>=2020." And Koha wants to let us use either a colon or an equals sign after our index name, so it always converts an equals sign in to a colon, which means our query turns into "pubdate:>:2020" and we get an error.