Go to Configuration > Payment and Shipping
Gateways and click to edit Bitcoin. You should ensure that
Bitcoin is turned 'ON' (or set to TEST or FAKE for testing). Your
settings should look similar to the following:
The ProcessCurrency MUST be BTC. This ensures
that orders are converted to the right value in Bitcoin at
checkout.
BitcoinRPCHost,
BitcoinRPCPort, BitcoinRPCUser
and BitcoinRPCPassword should all match
the ones you configured in the Bitcoin.conf file, see @17.6.3. Setting up the Bitcoin client