Update docs/references/protocol/transactions/types/nftokenmodify.md

Co-authored-by: oeggert <117319296+oeggert@users.noreply.github.com>

Author: DennisDawson

docs/references/protocol/transactions/types/nftokenmodify.md

@@ -35,5 +35,10 @@ title:
 | `Owner`           | String              | AccountID        | Address of the owner of the NFT. |
 | `NFTokenID`       | String              | Hash 256         | Composite field that uniquely identifies the token. |
 | `URI`             | String | Blob | _(Optional)_ Up to 256 bytes of arbitrary data. In JSON, this should be encoded as a string of hexadecimal. You can use the [`xrpl.convertStringToHex`](https://js.xrpl.org/modules.html#convertStringToHex) utility to convert a URI to its hexadecimal equivalent. This is intended to be a URI that points to the data or metadata associated with the NFT. The contents could decode to an HTTP or HTTPS URL, an IPFS URI, a magnet link, immediate data encoded as an [RFC 2379 "data" URL](https://datatracker.ietf.org/doc/html/rfc2397), or even an issuer-specific encoding. The URI is not checked for validity. |
+## Error Cases
+Besides errors that can occur for all transactions, {% $frontmatter.seo.title %} transactions can result in the following [transaction result codes](../transaction-results/index.md):
 
+| Error Code                   | Description |
+|:-------------------------|:-------------|
+| `tecNO_PERMISSION` | The `tfMutable` flag wasn't enabled, so you can't update the `URI` field. You can also receive this error if the `Account` field isn't an issuer or authorized minter of the NFT.  |
 {% raw-partial file="/docs/_snippets/common-links.md" /%}