Re: Origin In Game has been disabled in the Origin Client.

Hi  - In Origin, right-click the SimCity icon, choose Game Properties, and check the box to Enable Origin In Game. That should allow you to download the Nissan Leaf. You can change the option back and disable Origin in-game after you download the add-on. Sometimes disabling Origin in game helps performance of the game, so if you're not using the chat feature, no real reason to have it turned on.

The error message saying that you can't take over a city because you don't have all the content that was used to create it is probably not going to be solved by getting the Nissan Leaf, though. Unfortunately, this is something that happens a lot with abandoned cities. The problem is that there were a few add-ons that were never made available to everyone and there's no way to get them now. I wrote a post some time ago asking that EA make promo and region-specific add-ons available to everyone to help get rid of this problem, but chances are pretty slim that they would put any effort into it now. You could post a reply in the thread https://answers.ea.com/t5/SimCity-2013/Request-to-EA-Make-Promo-AddOns-Available/m-p/6652082, it would be great if we could get some traction on the problem. 

There are a bunch of things that someone may have in their version that you can't get any more. There was the Launch Arcology, which was only given to people who pre-ordered Cities of Tomorrow expansion pack. There was a free Progressive Insurance add-on, like the Nissan Leaf one, but it was only available for a limited time and is no longer accessible. There was a Crest/Oral-B add-on for people who got a special code from toothpaste boxes.

The biggest culprits, probably, are the country-specific add-ons for Germany, Sweden, Poland and France. I think these are still available automatically in those countries. So, technically, you can still get these, but it requires using a proxy server to make it look like you're logging in from each of those countries. Then you would go download the add-ons for that country; once you have them all enabled in your game, they will stay that way and you can just use the game normally from your own country. 

If anyone playing the game has any of these that you don't have, the game will interpret it as not having everything needed to take over the city and throw out the error. It's truly annoying and I wish they would either turn on the switches for everyone, or add them to the store so we could download them for free. I hope that helps you understand the error. Happy Building!