Refresh Fail - Folder Source

I have a PBIX file with a folder as the data source. The folder gets freshly exported csv files from a web service weekly. My expectation is that when the folder gets a new file added, the data modeling steps performed on the first will be applied to all subsequent.

I have published the pbix file to my dashboard and have set it to stay up to date. The actual pbix file lives on my one drive for business.

I am receiving the following error when refreshing on demand- I'm not sure what the error message means. Any help or pointers in the right direction are appreciated.

I should add that I am able to open the pbix file, and when I select refresh- it processes the data fine- and the visualizations are then up to date.