Some Zoho bills not exporting through API due to GST error

Some Zoho bills not exporting through API due to GST error

We are getting below error when trying to export bill for an unregistered GST vendor. We apply a GST expemption for these vendors. I believe this was working without issues few days ago. But now we get below error-

code: 71510,
  message: 'Tax Exemption should not be applied for GST unRegistered vendors Transaction.' }


What does this mean? How do we not charge GST for these vendors?

We have to pay our vendors in 2 days and  most of the bills are incorrect. PLEASE TAKE A LOOK.
The data sent through API-

{ vendor_id: '332408000014194195',
  bill_number: 1002227,
  source_of_supply: 'KA',
  destination_of_supply: 'KA',
  gst_treatment: 'business_none',
  contact_category: 'business_none',
  line_items:
   [ { account_id: '332408000000060017',
       description: 'Attachment payment for 6 days',
       rate: 7800,
       quantity: 1,
       item_order: 1,
       tax_exemption_id: '332408000008683617',
       tax_exemption_code: 'GST EXEMPTION' },
     { account_id: '332408000000060017',
       description: 'KM payment for total of 361 kms',
       rate: 0,
       quantity: 1,
       item_order: 2,
       tax_exemption_id: '332408000008683617',
       tax_exemption_code: 'GST EXEMPTION' },
     { account_id: '332408000000060017',
       description: 'Overtime payment',
       rate: 200,
       quantity: 1,
       item_order: 3,
       tax_exemption_id: '332408000008683617',
       tax_exemption_code: 'GST EXEMPTION' },
     { account_id: '332408000000060017',
       description: 'Return Distance/Bonus payment',
       rate: 50,
       quantity: 1,
       item_order: 4,
       tax_exemption_id: '332408000008683617',
       tax_exemption_code: 'GST EXEMPTION' } ],
  reference_number: 59eee37801a1e5ec2bdab79c,
  custom_fields: [ { index: 1, value: 59eee37801a1e5ec2bdab79c } ] }

Response:

{ code: 71510,
  message: 'Tax Exemption should not be applied for GST unRegistered vendors Transaction.' }