starts with xprv and when entered on the Import Bitcoin addresses or private keys screen on Electrum the "Next" button is grayed out.
the links from bitpay explaining how to get the private key are unnecessary as the app has a simple button to export the private key so there is no need to do that long drawn out process - that being said - I did it yesterday anyways and it just provided me the same private key that the app does. Again, I believe I stated this above.
If it starts with xprv, then that's basically your wallet's master private-key. You need to select Standard Wallet -> Use a master key; then paste it in there and click Next. That should work.