SELECT 
  cscart_payments.payment_id 
FROM 
  cscart_payments 
WHERE 
  cscart_payments.cp_rest_def = 'Y' 
  AND cscart_payments.status = 'A' 
  AND cscart_payments.payment_id NOT IN ('')

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_payments",
      "access_type": "ALL",
      "possible_keys": ["PRIMARY"],
      "rows": 14,
      "filtered": 100,
      "attached_condition": "cscart_payments.cp_rest_def = 'Y' and cscart_payments.`status` = 'A' and cscart_payments.payment_id <> ''"
    }
  }
}