For better or worse, technical interviews are the most important component of getting hired. As an economist, you're theoretically being hired to do a job with specialized skills. If you can't convince people you have those specialized skills, then why would they hire you?
The good news is that you don't need a perfect technical interview to get hired. With a 'decent' technical interview and a strong behavioral interview you'll be fine. The problem, of course, is that 'decent' is a concept that varies entirely in the mind of the interviewer. So the same interview would not just be scored differently across interviewers - it would be scored differently within a single interviewer over time.
Yes, there's randomness in the process. I've seen this firsthand and many people from other companies have admitted that hiring is inexact. I say all this to tell you that, if there's one company you really love, you may have to apply there multiple times even if you're a great candidate.
All of that is to say, more hopefully, that the law of large numbers will work for you eventually. It's the goal of this website to help you find the job you want in the minimal number of tries.
Now, let's get to the specifics. Like any other interview, there are two components to passing a technical interview.
1) Knowing what you're talking about.
2) Succinctly conveying what you know in a way that reaches the audience.
There's no substitute for the hours of hard work required for (1). However, you do need to know how to spend those hours. With that in mind, I've got two reading lists for you depending on your current specialization.
For people with a background in program evaluation (e.g. Development, Labor, Health, etc.), here's a reading list for you. My background is in program evaluation / causal analysis, and this was the core reading list I used to prepare for my tech interviews (I've since updated it with a few new papers, but the material covered is still similar).
I also have a good deal of forecasting experience, mostly in machine learning but also some time series. However, that was mostly acquired by Wikipedia and working with with others. So I had an excellent forecaster I know put together this reading list for you.
For empirical industrial organization, I've very little experience. Luckily, a generous compatriot who has quite a bit put together this reading list.
Once you're familiar with the core concepts covered here (at least, for your primary field) - or if you're interviewing tomorrow - you can look at the Technical Interview Framework section to see how to best apply them.