Next steps for troubleshooting a vague error like this would be to examine your inputs.
Are you setting your file name dynamically? (If not, it may be failing because you're trying to create multiple files with the same name.)
If you are able to, post a screenshot of the flow in edit mode, so we can see what data you're using in the Create File action.
One other method of troubleshooting is to go to the All Runs area of the flow, and then click the "Get .csv file" button. This will give you a spreadsheet that contains a lot more information about the inputs, outputs and errors in your flow. You may be able to find a more helpful error message than Bad Request there.

