Applying to an Econ PhD program as a software engineer? I'm in a similar situation as this poster: https://economics.stackexchange.com/questions/16428/career-change-to-economics-from-software-engineering , but it doesn't look like anyone answered about grad school admissions there. I have math and CS degrees from a top school, and if I could go back I would have taken classes and research in economics, but since I've already graduated and been working for 2 years, I feel like I've missed that opportunity. I'm self-studying economics right now, but what are some ways I could get experience that would be good for a grad school application?

I'm very interested in development economics, public policy, health economics, and behavioral economics and I know what my dream research groups and research directions are, if I can get the right skills/credentials.
Disclaimer: I'm not in economics

You might consider applying for a MS degree first. I don't know about economics, but I know that in my field at my university, we are a little more selective about Ph.D. admissions versus MS admissions, having something like twice as many MS candidates as Ph.D. candidates. If you otherwise had good GPA and good test scores, you can probably get into an MS degree at a decent school, although maybe not your dream school.  If you can exceed at the MS degree, get a publication or two and network at a few conferences, then you've got a much better shot at a top ranked Ph. D. program.