For each organization, there is a fee address associated with it. This fee address is used to pay for network fees for sending a transaction as well as create receive addresses. You must ensure that your fee address has a minimum balance of at least 0.05 eth. In the web UI, the fee address can be found on the transactions page.  If you are an API user, you can find the fee address inside the “coinSpecific” Object when you fetch the wallet.