Newdex api_key needs to be binded with EOS account. Apply for Newdex Market API_KEY
Since Newdex is a decentralized exchange and place order needs signature using user’s private key, while Newdex keeps clear of user’s private key, the Trade API does not include API of placing order. Users need to implement the order logic by their own. For more details please refer to How to Place Order on Newdex through Coding
Execute contract: cleos push action newdexpublic cancelorder '{"pair_id": "$pair_id","order_id": $order_id}' -p $your_account
Please stay tuned