What does "draw on us at 30 days" means here : (it's a confirmation of the terms of payment) "As agreed you will draw on us at 30 days, D/A, with the documents being sent to our bank."
Does it mean that the payment has to be done within 30 days?
The person writing "draw on us" is paying the other party. I'm not sure about the terms, but it looks to me as if the agreement was that the money would not be withdrawn any earlier than 30 days (after some point). In other words, at least 30 days has to pass after some point in time. There is not enough context here to know what point in time is.
It sounds as though the buyer, not the seller, wrote this. Please confirm.
"D/A" in finance means Documents Against Acceptance. It refers to shipping documents that the seller will send to the buyer's bank. The bank will hold them until the customer has accepted the merchandise. When that happens, the buyer's bank starts counting. At 30 days, the seller can get its money.