Based on your query you are not required any array index. The following is right index. You can use https://index-advisor.couchbase.com/indexadvisor/#1
CREATE INDEX ix1 ON stitchit_data_bucket (store_id ,date )
WHERE type = "invoice"
Check example 4 on query and index on nested arrays
https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/indexing-arrays.html#examples