Error message at API connector Bulk post

I defined the parameters , but initialize do not pass ,
attached the Entity data types , API parameters , and the error message ,
please help

The error already tell you what to do. Add header for content-type with value plain/text

Also, if your goal is to use bulk data, look at documentation carefully because your actual settings will.not work for more than 1 item

Thanks for the new response , I am using backend flow to insert mylty records in student_attendance table but it is very slow , so I’am trying to replace it with bulk insert ,
any reference or example for to do bulk insert , I’ve read the documentation but it is not clear there !!

Added the header but still getting the same ! any idea what I’am missing ?