# unapply_transfer · FT4 Rell API · Chromia Docs (concept)

> @mount("ft4.crosschain.unapply_ transfer")
operation unapply_ transfer(init_ transfer_ tx: gtx_ transaction, init_ tx_ op_ index: integer, last_ tx: gtx_ t

Source: https://docs.chromia.com/pages/ft4-rell/-f-t4-library/lib.ft4.external.crosschain/unapply_transfer/

OPERATION

# unapply\_transfer

```signature
@mount("ft4.crosschain.unapply_transfer")
operation unapply_transfer(init_transfer_tx: gtx_transaction, init_tx_op_index: integer, last_tx: gtx_transaction, last_op_index: integer, hop_index: integer)
```

[Source](https://gitlab.com/chromaway/ft4-lib/-/blob/development/rell/src/lib/ft4/external/crosschain/operations.rell#lines-540)

Unapplies a crosschain transfer that has expired. This operation must be called if
`apply_transfer` was already executed on this chain. To successfully unapply a transfer,
it must have been:

* canceled or any later hop (including the target chain), or
* recalled on the target chain.
  This operation should not be called on the init chain - `revert_transfer` should be used
  instead.

Throws `"INVALID TRANSFER"` if the transfer that is being unapplied was:

* never applied on this chain
* already canceled or unapplied

Throws `"INPUT ERROR"` if the input is malformed. This could be one of many different things:

* arguments found in `init_transfer_tx` and `last_tx` do not match
* `hop_index` is out of bounds or points to a different chain than this one
* `hop_index` points to the target chain, where canceling or recall should happen (not unapplying)
* `last_tx` has not been sent to the chain that comes after this one on the transfer hops

Throws`"UNSUPPORTED LAST OP"` if the operation found in `last_tx` at the given index is
neither of the three supported operations:

* `cancel_transfer` if the transfer was canceled before being applied on the chain that
  came after this one on the transfer hops
* `recall_unclaimed_transfer` if the transfer was applied on the target chain, it was sent
  to a non-existing account, and it has expired
* `unapply_transfer` if the transfer was canceled or recalled, and then unapplied on another
  chain before reaching this one

Throws `"TRANSFER NOT EXPIRED"` if the transfer being reverted did not expire

Throws if the `init_tx_op_index` does not point to `init_transfer` on `init_transfer_tx`

Throws if the required assets cannot be transferred. While this could throw in all cases
of misconfiguration considered possible for `apply_transfer`, to unapply a transfer it must
first have been applied. This means that the most probable scenario for the transfer of
funds to fail is if the sender blockchain account balance is lower than `amount`.

Other cases considered possible for `apply_transfer` are still possible, although unlikely.
For example, the asset entity could have been deleted, which means that the asset is no
longer registered on this chain.

Requires no flags - no authorization is performed to unapply a transfer.

**Parameters**

* **init\_transfer\_tx** — the transaction containing the `init_transfer` operation which corresponds to the transfer to unapply
* **init\_tx\_op\_index** — the index of the `init_transfer` operation in `init_transfer_tx`
* **last\_tx** — the last transaction in this transfer flow, as sent to the previous hop. Note that "previous" in this context refers to the chain at n + 1 in the hops array in relation to this blockchain, since we are walking the hops array backwards. It must contain one of the three supported operations described above.
* **last\_op\_index** — the index of the supported operation in `last_tx`
* **hop\_index** — which index in the hops array provided in the original transaction this chain represents.

**See Also**

* [apply\_transfer](https://docs.chromia.com/pages/ft4-rell/-f-t4-library/lib.ft4.external.crosschain/apply_transfer/) — for edge cases where this operation might throw
* `core.crosschain.applied_transfers` — to know more about the crosschain transfer workflow
* `core.crosschain.unapplied_transfers` — to know more about transfer unapplying
* `core.crosschain.canceled_transfers` — to know more about transfer canceling
* `core.crosschain.recalled_transfers` — to know more about transfer recall

[View this page on docs.chromia.com](https://docs.chromia.com/pages/ft4-rell/-f-t4%20-library/lib.ft4.external.crosschain/unapply_transfer.html)Generated API reference, mirrored from the live docs