Unfortunately Easy Checkin will not work for the return leg of international itins that put you into a country other than one you hold a passport for. For example, I live in the UK but fly on a US passport, whenever I fly back from the UK from the US as part of a LHR-US and then US-LHR itin, easy checking never accepts my itin. Always says to see an agent. They need to see the Visa so that UA doesn't get stuck with flying me back and paying a fine