Attachment Body Type Error When Uploading Files to Salesforce with dataloader.io

In dataloader.io from Mulesoft, a task that inserts attachments fails with the error: “The attachment body has an incorrect type. Expected byte[] or InputStream.”

This issue occurs when the files listed in the CSV do not exactly match the files included in the ZIP file. Differences in file names (including case or special characters) or missing files can trigger this error.

Additionally, if the ZIP file contains a folder instead of the files directly at the root level, the task may fail with the same error.