Usually, the site search extension is compatible with the majority of custom themes right out of the box and doesn't require any additional tweaking. But in case there are any issues, our support specialists will eliminate them for free.
This is a common problem caused by MySQL configuration, and it’s connected with a minimum length of a search query.
Please check "ft_min_word_len" setting; it controls the minimum number of characters in the MySQL query. If you lower the limit, you will be able to search using three-letter (or fewer, if needed) queries with our Search Pro extension.