I looked up the website of the Journal of Post Keynesian Economics (JPKE) and it seems to be a specialized journal in the field of economics, catering to "innovative theoretical and empirical work that sheds fresh light on contemporary economic problems." From what I understood, the journal publishes work on economic theory that can influence public policy in some way. I think by "field journal" the editor is referring to a more generic journal in the field of economics. What is more important is that the journal you select should be a good match in terms of topic and methodological style.
So basically, you will need to come up with a list of reputable journals in economics and then go through the journal website to see if they are a good match for your paper. It's difficult for us to recommend a list of journals. However, you can check online for databases of economics journals. You can also conduct a search by subject in the Directory of Open Access Journals (DOAJ).
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