50% upon signing the contract and after pra shipment应该是：签订合同时付款50%,发货后付完余款.这个pra很难理解,最好问下发邮件的人,确保付款万无一失.
40% upon loading start to barge
10%upon completed loaded on MVessel应该是：货物开始装船时付款40%；装船后追加10%的付款.