It is strongly not recommended to initiate a payment through cryptocurrencies exchanges/web wallets such as Coinbase, Bittrex, etc. The reason is due to the significant delay and sometimes fees charged by the exchange. As a result, transactions often arrive too late (when the invoice has already expired) and / or not enough amount is sent (so the invoice is underpaid). This is why we recommend to use one of many opensource wallets, where you control the exact amount sent and when the transaction will be sent.
Please note that when you initiate a payment through CoinGate (our cryptocurrency gateway), you only have 20 minutes to complete the payment.
Furthermore, you do not control your own bitcoins when using a web wallet, so you introduce counterparty risk and thus negate one of the main benefits of cryptocurrencies - to be in full control of your own money.
To learn how you can install and configure a cryptocurrency wallet, visit a blog post by CoinGate here: https://blog.coingate.com/2017/01/bitcoin-wallet-guide/