You can only provide an external tax_mode when partially refunding.

{
  "error": {
    "type": "request_error",
    "code": "adjustment_tax_mode_not_allowed",
    "detail": "You're attempting to pass `tax_mode: external` with a `type` other than `partial` or an `action` other than `refund`.",
    "documentation_url": "https://developer.paddle.com/errors/adjustments/adjustment_tax_mode_not_allowed"
  },
  "meta": {
    "request_id": "00000000-0000-0000-0000-000000000000"
  }
}

Details

Status code

400

Error code

adjustment_tax_mode_not_allowed

Error message

You're attempting to pass `tax_mode: external` with a `type` other than `partial` or an `action` other than `refund`.

Common causes

• You're trying to create an adjustment where the tax_mode is external, but the type is full. Only partial refunds can be created using external tax amounts.
• You're trying to create an adjustment where the tax_mode is external, but the action is one other than refund. Only refunds can be created using external tax amounts.

Troubleshooting

• Ensure the type is partial and action is refund.
• Pass internal as the tax_mode to specify that amounts are inclusive of tax.