> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bolta.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Amendment Types

> How each type of tax invoice amendment works, with calculation examples.

## Cancellation of Contract

An amendment for the Cancellation of Contract reason carries only `date` (write date) and offsets the original issuance.

**Example**

| Category                           | Amount          |
| ---------------------------------- | --------------- |
| Original tax invoice               | KRW 50,000      |
| Cancellation of Contract amendment | **KRW -50,000** |

<Warning>
  If the item supply cost of the original tax invoice is negative, a Cancellation of Contract amendment is not allowed.
</Warning>

## Change in Supply Cost

An amendment for the Change in Supply Cost reason carries, as items, how much (+) or (-) the amount changed relative to the original.

For example, if you overstated an item's unit price by KRW 1,000, you issue it as -1,000.

<Info>
  Item input limits and [unsupported character](/en/docs/api-introduction/issuance-guide#unsupported-characters) handling are the same as for standard issuance. There must be between 1 and 16 items, and the item specification (`items[].specification`) is up to 60 characters. Also pass the tax type (`taxType`), and set the tax (`items[].tax`) as shown in the table below.
</Info>

| Tax type (`taxType`) | Item tax (`items[].tax`)                     |
| -------------------- | -------------------------------------------- |
| `TAXABLE`            | Pass a non-`null` value                      |
| `ZERO_RATE`          | Pass `0` for every item                      |
| `TAX_FREE`           | Pass `null` for every item or omit the field |

### Calculation example

**Original tax invoice**

| Item name   | Unit price (unitPrice) | Quantity (quantity) | Supply cost (supplyCost) | Tax (tax) | Amount (supplyCost + tax) |
| ----------- | ---------------------- | ------------------- | ------------------------ | --------- | ------------------------- |
| First item  | 5,000                  | 10                  | 50,000                   | 5,000     | 55,000                    |
| Second item | 3,000                  | 50                  | 150,000                  | 15,000    | 165,000                   |

**Change in Supply Cost amendment invoice** (carrying the difference)

| Item name   | Unit price (unitPrice) | Quantity (quantity) | Supply cost (supplyCost) | Tax (tax) | Amount (supplyCost + tax) |
| ----------- | ---------------------- | ------------------- | ------------------------ | --------- | ------------------------- |
| First item  | **-1,000**             | 10                  | -10,000                  | -1,000    | -11,000                   |
| Second item | **-1,000**             | 50                  | -50,000                  | -5,000    | -55,000                   |

**Final transaction amount**

| Item name   | Unit price (unitPrice) | Quantity (quantity) | Supply cost (supplyCost) | Tax (tax) | Amount (supplyCost + tax) |
| ----------- | ---------------------- | ------------------- | ------------------------ | --------- | ------------------------- |
| First item  | 4,000                  | 10                  | 40,000                   | 4,000     | 44,000                    |
| Second item | 2,000                  | 50                  | 100,000                  | 10,000    | 110,000                   |

## Double Issuance by Mistake

An amendment for the Double Issuance by Mistake reason is called without any request parameters and offsets the original issuance. The write date of the original tax invoice is applied automatically.

**Example**

| Category                             | Amount          |
| ------------------------------------ | --------------- |
| Original tax invoice                 | KRW 50,000      |
| Double Issuance by Mistake amendment | **KRW -50,000** |