If you are seeing this error code message,
“The Relationship Type field heading is invalid, so values in this field were ignored. To correct this error, download the template again and use the new copy, or fix the field heading in your existing file.”
Amazon probably updated the current template you are using, so you are receiving a parsing error.
After downloading the template from Amazon seller central,
1- Click “Edit Template” from the actions tab.
2- Upload the template you have downloaded.
3- Check all remote fields and update the valid values.
4- Send product data update and sync the channel.