what expense account should I use to add non US contractors payment?

You can check the following reference. You do not need to differentiate between US contractors and non-US contractors, unless you have other specific concerns.

https://quickbooks.intuit.com/learn-support/en-us/help-article/pay-bills/enter-bills-record-bill-payments-quickbooks-online/L1e9Ce5J7_US_en_US?uid=lqnos39y

You should also consider using Melio to pay your international contractors. Their exchange rates are better than MoneyGram. You can signup for a free Melio account to integrate with QBO and their flat fee is $20 per transaction.

https://affiliates.meliopayments.com/quickbooks

You can get $100 cashback to pay the first bill.

https://affiliates.meliopayments.com/cashback