I can't find much about the Carter Foundation, but Edison Polling—the organization that released the exit poll that showed the opposition winning— does have a long history of criticism for being US-backed and consistently producing results that favor US interests.

Meanwhile, the most respected pollster in the country, Hinterlaces, released an exit poll that estimated right around the actual results (54% vs 51%)

https://x.com/Hinterlaces/status/1817599369471799639

In addition, there are plenty of other international observers that back the result. Like the National Lawyers Guild

https://nlginternational.org/2024/07/press-release-national-...