Hello, @dusterthomas.
Can you specify, where exactly did you receive this error?
To export maps or markers, you should press on export button – does 403 error appear exactly after this? If so, I recommend you to write us via internal support to investigate such kind of issue in more details.
At this moment, you can try to check conflicts with other plugins or your theme as a general suggestion. Please try to deactivate all your plugins one by one and check the issue. Thus you will find out which plugin causes the error. If it won’t help, try to switch temporarily to a standard WordPress theme.
More useful information you can find here: https://supsystic.com/tips-for-solving-issues-faster/