diff --git a/core/archipelago/src/wallet/cashu.rs b/core/archipelago/src/wallet/cashu.rs
index 936e0155..762e14de 100644
--- a/core/archipelago/src/wallet/cashu.rs
+++ b/core/archipelago/src/wallet/cashu.rs
@@ -215,12 +215,56 @@ impl CashuToken {
                 if proof.c.is_empty() {
                     anyhow::bail!("Proof has empty C");
                 }
+                validate_keyset_id(&proof.id)?;
             }
         }
         Ok(())
     }
 }
 
+/// NUT-02 keyset ID: hex for either 8 bytes (v1, the `00…` short form) or
+/// 33 bytes (v2, version-byte + hash).
+///
+/// Checked when a token is decoded rather than left to the mint. Forwarding
+/// an out-of-spec id produced a swap the mint rejected with a bare
+/// `422 Unprocessable Entity`, which reached the operator as "check server
+/// logs" with nothing actionable in the UI (framework-pt, 2026-08-17,
+/// mint.minibits.cash: `inputs[0].id: NUT02: ID length invalid`). A local
+/// check can say which keyset format the token uses and that this wallet
+/// cannot spend it, before any network call.
+fn validate_keyset_id(id: &str) -> Result<()> {
+    let bytes = hex::decode(id).map_err(|_| {
+        anyhow::anyhow!(
+            "Token uses a keyset id that is not hex ({id:?}) — this wallet supports \
+             NUT-02 v1 (8-byte) and v2 (33-byte) hex keyset ids"
+        )
+    })?;
+    match bytes.len() {
+        // 8 bytes is v1's whole id, and also what a wallet that predates v2
+        // leaves behind when it truncates one. Both are accepted here; the
+        // truncated case is repaired against the mint's keyset list at swap
+        // time (see MintClient::resolve_truncated_keyset_ids).
+        8 | 33 => Ok(()),
+        n => anyhow::bail!(
+            "Token uses an unsupported keyset id format: {n}-byte id {id:?}. NUT-02 \
+             defines 8-byte (v1) and 33-byte (v2) ids; the mint will reject a swap \
+             carrying this one"
+        ),
+    }
+}
+
+/// Is this the first 8 bytes of a NUT-02 **v2** keyset id rather than a
+/// complete v1 one?
+///
+/// A v1 id is 8 bytes beginning with the version byte `0x00`; a v2 id is 33
+/// bytes beginning with `0x01`. So an 8-byte id that starts with `0x01` is a
+/// v2 id some wallet cut to the old length — it cannot be spent as-is, but
+/// the full id can be recovered from the mint because the short form is a
+/// prefix of it.
+pub fn is_truncated_v2_keyset_id(id: &str) -> bool {
+    id.len() == 16 && id.starts_with("01") && hex::decode(id).is_ok()
+}
+
 /// Decode a token's base64 payload, trying URL-safe-no-pad first (the spec
 /// default) and falling back to other alphabets some implementations use.
 fn decode_token_base64(payload: &str) -> Result<Vec<u8>, base64::DecodeError> {
@@ -473,4 +517,66 @@ mod tests {
         };
         assert!(proof.c_as_pubkey().is_ok());
     }
+
+    #[test]
+    fn keyset_ids_of_both_nut02_versions_are_accepted() {
+        // v1: 8 bytes / 16 hex chars.
+        assert!(validate_keyset_id("009a1f293253e41e").is_ok());
+        // v2: 33 bytes / 66 hex chars (version byte + 32-byte hash).
+        let v2 = format!("01{}", "ab".repeat(32));
+        assert!(validate_keyset_id(&v2).is_ok());
+    }
+
+    #[test]
+    fn a_truncated_v2_keyset_id_is_recognised_as_repairable() {
+        // The real case: a Minibits token carried the first 8 bytes of the
+        // mint's 33-byte v2 keyset id (2026-08-17).
+        let short = "01fc0ec0e59cd6fa";
+        let full = "01fc0ec0e59cd6fa01b7a88f8cd77fce81fd1e64bca67d752e984992b7a3c3a821";
+        assert!(is_truncated_v2_keyset_id(short));
+        assert!(full.starts_with(short), "short form must prefix the full id");
+        // It must survive token validation so the swap path can repair it,
+        // rather than being rejected as malformed.
+        assert!(validate_keyset_id(short).is_ok());
+
+        // A genuine v1 id (version byte 00) is not "truncated".
+        assert!(!is_truncated_v2_keyset_id("009a1f293253e41e"));
+        // Neither is a complete v2 id.
+        assert!(!is_truncated_v2_keyset_id(full));
+    }
+
+    #[test]
+    fn an_out_of_spec_keyset_id_is_rejected_locally_with_its_length() {
+        // 9 bytes — what a legacy base64 keyset id decodes to, and neither
+        // NUT-02 length. The mint answers this with a bare 422, so the
+        // message has to come from here.
+        let err = validate_keyset_id("00112233445566778899")
+            .expect_err("9-byte keyset id must be rejected");
+        let msg = err.to_string();
+        assert!(msg.contains("10-byte") || msg.contains("unsupported keyset id"), "{msg}");
+
+        // Non-hex ids (the original base64 keyset format) are named as such
+        // rather than reported as a length problem.
+        let err = validate_keyset_id("I2yN+iRYfkzT").expect_err("base64 id must be rejected");
+        assert!(err.to_string().contains("not hex"), "{err}");
+    }
+
+    #[test]
+    fn a_token_carrying_an_unsupported_keyset_id_fails_to_decode() {
+        let token = CashuToken {
+            token: vec![TokenEntry {
+                mint: "https://mint.example.com".to_string(),
+                proofs: vec![Proof {
+                    amount: 1,
+                    id: "I2yN+iRYfkzT".to_string(),
+                    secret: "s".to_string(),
+                    c: "02".to_string(),
+                }],
+            }],
+            memo: None,
+            unit: None,
+        };
+        // The whole point: this must fail here, not at the mint.
+        assert!(token.validate().is_err());
+    }
 }
diff --git a/core/archipelago/src/wallet/mint_client.rs b/core/archipelago/src/wallet/mint_client.rs
index e92a6374..e5df450f 100644
--- a/core/archipelago/src/wallet/mint_client.rs
+++ b/core/archipelago/src/wallet/mint_client.rs
@@ -9,7 +9,8 @@
 
 use super::bdhke;
 use super::cashu::{
-    amount_to_denominations, BlindSignature, BlindedMessageRequest, CashuToken, MintKeyset, Proof,
+    amount_to_denominations, is_truncated_v2_keyset_id, BlindSignature, BlindedMessageRequest,
+    CashuToken, KeysetInfo, MintKeyset, Proof,
 };
 use anyhow::{Context, Result};
 use serde::{Deserialize, Serialize};
@@ -184,6 +185,31 @@ impl MintClient {
         Ok(keysets)
     }
 
+    /// List the mint's keysets (NUT-02 `GET /v1/keysets`) — ids and status
+    /// only, no public keys. Unlike `/v1/keys` this includes *inactive*
+    /// keysets, which a received token may well reference: coins from a
+    /// retired keyset stay spendable.
+    pub async fn get_keysets(&self) -> Result<Vec<KeysetInfo>> {
+        let url = format!("{}/v1/keysets", self.url);
+        let res = self
+            .client
+            .get(&url)
+            .send()
+            .await
+            .context("Failed to fetch mint keysets")?;
+        if !res.status().is_success() {
+            anyhow::bail!("Mint keysets request failed: {}", res.status());
+        }
+        let body: serde_json::Value = res.json().await.context("Failed to parse mint keysets")?;
+        let keysets: Vec<KeysetInfo> = serde_json::from_value(
+            body.get("keysets")
+                .cloned()
+                .unwrap_or(serde_json::json!([])),
+        )
+        .context("Failed to parse keyset list")?;
+        Ok(keysets)
+    }
+
     /// Get the active keyset for the "sat" unit.
     pub async fn get_active_sat_keyset(&self) -> Result<MintKeyset> {
         let keysets = self.get_keys().await?;
@@ -483,6 +509,61 @@ impl MintClient {
 
     /// Receive a CashuToken by swapping its proofs for fresh ones.
     /// This prevents double-spend and ensures only we can spend the new proofs.
+    /// Repair proofs whose keyset id is a truncated NUT-02 **v2** id.
+    ///
+    /// A v2 keyset id is 33 bytes (version byte `0x01` + 32-byte hash), but
+    /// wallets written against the original 8-byte format truncate it when
+    /// they build a token. The mint then reads the `0x01` version, expects 33
+    /// bytes, and rejects the swap — reported as
+    /// `inputs[0].id: NUT02: ID length invalid` behind a bare 422 (seen with
+    /// a Minibits-issued token, 2026-08-17).
+    ///
+    /// The id only names which keyset signed the proof, so restoring the full
+    /// id the mint advertises is exactly what the sender meant. It is also
+    /// safe to attempt: an id that names the wrong keyset fails signature
+    /// verification at the mint and no coins move. Anything already valid, or
+    /// with no unambiguous match, is passed through untouched so the mint's
+    /// own error is what the operator sees.
+    async fn resolve_truncated_keyset_ids(&self, proofs: &[Proof]) -> Vec<Proof> {
+        let needs_repair = proofs.iter().any(|p| is_truncated_v2_keyset_id(&p.id));
+        if !needs_repair {
+            return proofs.to_vec();
+        }
+
+        let known = match self.get_keysets().await {
+            Ok(k) => k,
+            Err(e) => {
+                debug!("Could not list keysets to repair truncated keyset ids: {e:#}");
+                return proofs.to_vec();
+            }
+        };
+
+        proofs
+            .iter()
+            .cloned()
+            .map(|mut p| {
+                if !is_truncated_v2_keyset_id(&p.id) {
+                    return p;
+                }
+                // Prefer an active keyset when a prefix somehow matches more
+                // than one; ambiguity beyond that is left to the mint.
+                let mut matches = known
+                    .iter()
+                    .filter(|k| k.id.len() == 66 && k.id.starts_with(&p.id))
+                    .collect::<Vec<_>>();
+                matches.sort_by_key(|k| !k.active);
+                if let Some(full) = matches.first() {
+                    debug!(
+                        "Expanded truncated v2 keyset id {} to {} for swap",
+                        p.id, full.id
+                    );
+                    p.id = full.id.clone();
+                }
+                p
+            })
+            .collect()
+    }
+
     pub async fn receive_token(&self, token: &CashuToken) -> Result<Vec<Proof>> {
         let mut all_new_proofs = Vec::new();
 
@@ -498,7 +579,8 @@ impl MintClient {
             let total: u64 = entry.proofs.iter().map(|p| p.amount).sum();
             let target_amounts = amount_to_denominations(total);
 
-            let result = self.swap(&entry.proofs, &target_amounts).await?;
+            let proofs = self.resolve_truncated_keyset_ids(&entry.proofs).await;
+            let result = self.swap(&proofs, &target_amounts).await?;
             all_new_proofs.extend(result.new_proofs);
         }