Elasticsearch "illegal_argument_exception" when trying to search by string type

Most likely one of your int or decimal attributes is searchable. Try to find them by using the following SQL query:

SELECT * FROM eav_attribute e
LEFT JOIN catalog_eav_attribute cea ON e.attribute_id = cea.attribute_id
WHERE e.backend_type = 'decimal'
AND cea.is_searchable = 1
AND e.frontend_input != 'price';

If you find decimal attribute which is searchable try to make it as Not Searchable

• Go to admin -> store -> attributes -> product -> find the attribute
• Edit attribute and make it NOT Searchable
• Run full reindex php bin/magento index:reinde catalogsearch_fulltext

This issue may occurs when you are using an older version of Elastic search. For example Magento 2.3 comes with Elasticsearch and Elasticsearch 5.0+ versions. You must have elasticsearch 5 installed as engine and select the Elasticsearch 5.0+ as search engine in Magento admin.

Furthermore as of time of writing I have found out that Elasticsearch 6 doesn't cope well with Magento. Elasticsearch 5 is fine.

I had the same problem with search string. With ES 2.4.6.I solved it change property of an attribute datetype to NOT use in search. I saw that there is an issue with date maping (when searching by string)