Why is my ShapeShift transaction being denied?

Question

I'd really like to to exchange BTC for XMR. I'm attempting a transaction via Circle.com to ShapeShift.io according to this guide:
https://forum.getmonero.org/5/support/2384/the-easiest-way-to-buy-monero

Circle is currently taking hours to process, only to inform me that it fails. I've only ever exchanged USD to BTC before, so this is my first time exchanging BTC for another currency.

Being unable to find simple, straightforward exchange is a barrier to using these currencies. I'm not looking to be a trader. I just want to exchange BTC for XMR the easiest way possible. I don't know why the exchange from Circle to ShapeShift is failing, but I need something that works.

Is there some alternative method to easily exchange BTC to Monero?

Update: While the selected answer is correct regarding the time limits, this problem is directly related to Circle dot com failing to complete BTC transactions. I have not been able to access my funds since creating an account with them. As for the Monero guide linked to here, I highly recommend using another option if you need to purchase BTC before exchanging for XMR.

Update II: The delays were entirely due to account verification being incomplete. I have since tested and precise ShapeShift transfers are successful and quick.

Answer 1

Circle is currently taking hours to process

There is nothing wrong with using Shapeshift to exchange BTC for XMR. The problem you are having is because of your use of a 3rd party wallet and the resulting inability to reliably send a transaction without delay. According to your comments below I understand you were using the "precise" Shapeshift conversion option which you correctly noted enforces a 10 minute time limit.

Using 3rd party wallet providers can lead to transaction delays for any number of reasons including a sudden spike in user transactions requiring more funds being to be moved from cold storage.

Circle is a 3rd party wallet where it controls your private keys as can be seen from clicking the Circle description on the bitcoin.org choose your wallet page:

Money controlled by a third party

This service has full control over your bitcoins. This means you need to trust this service will not freeze or mismanage your funds. Although this service claims to be providing insurance against failures on their side, you are still responsible for securing your wallet.

Look for wallets where you control the private keys. When you control your private keys, no 3rd party can delay or prevent you from submitting a transaction to the Bitcoin network.

Bitcoin Core is one of many wallets where you have full contol of your Bitcoin:

Control over your money

This wallet gives you full control over your bitcoins. This means no third party can freeze or lose your funds. You are however still responsible for securing and backing up your wallet.

In addition to possible transaction delays (and security concerns) when relying on 3rd party wallets you are also subjecting yourself to censorship. Reddit has countless examples of Coinbase and to a lesser extent Circle accounts being closed because of blockchain analysis. Even if you do nothing to violate the ToS of the 3rd party wallet provider, the parties you send Bitcoin to (or receive Bitcoin from) might thereby giving justification for your account to be closed.