Database
db={"paid":[{"_id":{"$oid":"60aba58c5eff5afbc6e7c9f3"},"created":{"$date":{"$numberLong":"1621861772297"}},"questionId":{"$oid":"60ab8e0c485bfcf514e0bc18"},"userId":"gctqXxSIrAe8O8HidhOhxzYIDjR2"}],"question":[{"_id":{"$oid":"60ab8e0c485bfcf514e0bc18"},"created":{"$date":{"$numberLong":"1621855756763"}},"clientId":"ksCBoGLIr7MPNcod2FqXNPNcgZj2","topic":"Engineering"}]}
Query
db.paid.aggregate([{"$lookup":{"from":"question","localField":"questionId","foreignField":"_id","as":"output"}}])