While creating a child table supplier in the material request this exception is throwing

1 
frappe.exceptions.ValidationError: Supplier: [{"docstatus":0,"doctype":"Material Request Supplier","name":"new-material-request-supplier-1","__islocal":1,"__unsaved":1,"owner":"Administrator","quote_status":"Pending","send_email":1,"email_sent":0,"parent":"MAT-MR-2021-00002-1","parentfield":"supplier","parenttype":"Material Request","idx":1,"__unedited":false,"supplier_name":"supplier2","supplier":"supplier2"}] does not exists