diff --git a/README.md b/README.md
index 2849bd6..94a169f 100644
--- a/README.md
+++ b/README.md
@@ -119,10 +119,14 @@ client.payments.submit_by_hash(rail0_id, "capture", { transaction_hash: "0x…"
 | `dispute_submit_by_hash` / `close_dispute_submit_by_hash` | payer | Report a dispute tx the wallet already broadcast |
 
 **Payment statuses:** `unsigned`, `signed`, `authorized`, `charged`, `captured`,
-`partially_captured`, `voided`, `released`, `refunded` — plus `partially_refunded`,
-which is no longer produced (a partial refund deliberately leaves the status alone)
-but is still a legal value on historical rows, so don't write an exhaustive `case`
-that raises on it.
+`partially_captured`, `voided`, `released`, `refunded`, `expired` — plus
+`partially_refunded`, which is no longer produced (a partial refund deliberately leaves
+the status alone) but is still a legal value on historical rows, so don't write an
+exhaustive `case` that raises on it.
+
+`expired` is a never-captured authorization whose window lapsed. It is **not** terminal:
+the escrow is still on-chain and `release` still works from it (closing the payment as
+`released`), so treating it as closed leaves the buyer's funds where they are.
 **Transaction statuses:** `pending`, `submitting`, `submitted`, `confirmed`, `failed`.
 
 ## Authentication (SIWE)
diff --git a/lib/rail0/error_hints.rb b/lib/rail0/error_hints.rb
index 354d1d9..4f99fd5 100644
--- a/lib/rail0/error_hints.rb
+++ b/lib/rail0/error_hints.rb
@@ -20,6 +20,16 @@ module Rail0
     "nothing_to_dispute" => "a dispute needs a merchant-held (refundable) balance",
     "transaction_not_overwritable" => "a transaction for this operation is already in flight — wait for it to settle",
     "signer_mismatch" => "the signing key doesn't match the payment's payer/payee",
+    # The SIWE BINDING failures, split out of signer_mismatch so a failed login says
+    # WHICH part of the proof did not bind (#216). None names the server's own
+    # expectation: that endpoint is unauthenticated, so echoing the allow-list or the
+    # expected chain id would turn every hint into a probe.
+    "siwe_domain_not_allowed" => "sign with the origin the front-end is served from, and have it added to the gateway's SIWE domain allow-list",
+    "siwe_uri_mismatch" => "the message's uri host must equal its own domain",
+    "siwe_chain_mismatch" => "use the chain id the client library sends - this login is off-chain and nominal",
+    "siwe_proof_expired" => "get a fresh nonce and sign again",
+    # Address-wide, not one token: "sign in again", not "that token is dead".
+    "sessions_revoked" => "every session issued before this address's revoke-all cutoff is refused - sign in again",
     "config_hash_mismatch" => "the payment record and its on-chain deployment disagree — the payment cannot be operated as recorded",
     "payment_not_on_chain" => "the contract has no record of this payment — its opening transaction may never have confirmed",
     "unsupported_contract_version" => "the payment's RAIL0 deployment is newer or older than this gateway supports — upgrade the gateway",
diff --git a/lib/rail0/request.rb b/lib/rail0/request.rb
index f2980d4..6fe7389 100644
--- a/lib/rail0/request.rb
+++ b/lib/rail0/request.rb
@@ -172,12 +172,17 @@ def parse_error_body(response)
       {}
     end
 
+    # The gateway answers exactly code/title/detail, having DELETED the older aliases
+    # rather than dual-sending them (#252) — `status` (the wider family), `message`
+    # (equal to detail) and Grape's `error`. The chains that read them could only ever
+    # find absent keys, so each collapses to the one field there is. The bare HTTP status
+    # stays as the last resort for a body with no text at all.
     def error_code(body)
-      body[:code] || body[:error] || body[:status]
+      body[:code]
     end
 
     def error_message(body, response = nil)
-      body[:detail] || body[:message] || body[:error] || (response && "HTTP #{response.code}")
+      body[:detail] || (response && "HTTP #{response.code}")
     end
 
     def elapsed_ms(start)
diff --git a/lib/rail0/types.rb b/lib/rail0/types.rb
index 43abb1a..f9c42cc 100644
--- a/lib/rail0/types.rb
+++ b/lib/rail0/types.rb
@@ -172,6 +172,10 @@ module Types
       :amount,                # String
       :capturable_amount,     # String — Mirrors on-chain capturableAmount (escrow still held); base units.
       :refundable_amount,     # String — Mirrors on-chain refundableAmount (held by payee, still refundable); base units.
+      # The window after a PARTIAL capture where neither void nor release can return the
+      # buyer's remaining escrow — the answer to "why did both just refuse?".
+      :escrow_stranded,       # Boolean
+      :escrow_returnable_at,  # String, nil — ISO-8601 end of that window; nil outside it.
       :config_hash,           # String
       :payer,                 # String
       :payee,                 # String
diff --git a/spec/client_spec.rb b/spec/client_spec.rb
index 10341cf..03e632d 100644
--- a/spec/client_spec.rb
+++ b/spec/client_spec.rb
@@ -179,7 +179,8 @@ def stub_patch(path, body, status: 200)
 
     it "raises Rail0::ApiError when the address is not registered" do
       stub_post("/auth/nonces", NONCE_RESPONSE, status: 201)
-      stub_post("/auth", { status: "address_not_registered", message: "Address is not registered." }, status: 403)
+      stub_post("/auth", { code: "address_not_registered", title: "Address not registered",
+                           detail: "Address is not registered." }, status: 403)
 
       expect { client.auth.login(private_key: key, domain: "api.rail0.xyz") }
         .to raise_error(Rail0::ApiError) do |err|
@@ -630,9 +631,9 @@ def stub_authed_get(token)
   # ── Error handling ─────────────────────────────────────────────────────────
 
   describe "error handling" do
-    it "raises Rail0::ApiError on 422 with status/message" do
+    it "raises Rail0::ApiError on 422 with code/detail" do
       stub_get("/payments/#{PAYMENT_ID}",
-               { status: "payment_not_found", message: "No payment exists for the given id." }, status: 422)
+               { code: "payment_not_found", detail: "No payment exists for the given id." }, status: 422)
       expect { client.payments.get(PAYMENT_ID) }
         .to raise_error(Rail0::ApiError) do |err|
           expect(err.status).to eq(422)
@@ -643,7 +644,7 @@ def stub_authed_get(token)
 
     it "raises Rail0::ApiError on a 422 state error" do
       stub_post("/payments/#{PAYMENT_ID}/capture",
-                { status: "not_capturable", message: "Payment is not capturable." }, status: 422)
+                { code: "not_capturable", detail: "Payment is not capturable." }, status: 422)
       expect { client.payments.capture(PAYMENT_ID, { signed_transaction: "0x02" }) }
         .to raise_error(Rail0::ApiError) { |err| expect(err.error).to eq("not_capturable") }
     end
@@ -691,7 +692,7 @@ def stub_authed_get(token)
       attempts = 0
       stub_request(:get, "#{BASE_URL}/payments/#{PAYMENT_ID}").to_return do
         attempts += 1
-        { status: 422, body: { status: "payment_not_found", message: "x" }.to_json, headers: json_headers }
+        { status: 422, body: { code: "payment_not_found", detail: "x" }.to_json, headers: json_headers }
       end
       retrying = Rail0::Client.new(base_url: BASE_URL, max_retries: 2, retry_delay: 0)
       expect { retrying.payments.get(PAYMENT_ID) }.to raise_error(Rail0::ApiError)
diff --git a/spec/errors_spec.rb b/spec/errors_spec.rb
index 5a31d35..fd57d71 100644
--- a/spec/errors_spec.rb
+++ b/spec/errors_spec.rb
@@ -34,9 +34,11 @@ def stub_error(status, body)
     expect(error.status).to eq(422)
   end
 
-  # An older gateway sends neither code nor detail: the specific condition arrives in
-  # `error` and the text in `message`. Both must still surface.
-  it "falls back to the pre-code/title/detail field names" do
+  # This used to assert the OPPOSITE: that an older gateway's `status`/`error`/`message`
+  # still surfaced. Those keys were deleted from the wire rather than dual-sent (#252),
+  # so what matters now is that a body carrying only them yields nothing pretending to be
+  # a code — a silent "" would be branched on as if it were a real condition.
+  it "does not invent a code from the deleted alias fields" do
     stub_error(422, { status: "invalid_state", error: "not_capturable", message: "no capturable balance" })
 
     error = begin
@@ -45,8 +47,8 @@ def stub_error(status, body)
       e
     end
 
-    expect(error.error).to eq("not_capturable")
-    expect(error.detail).to eq("no capturable balance")
+    expect(error.error).to be_nil
+    expect(error.detail).to eq("HTTP 422")
     expect(error.title).to be_nil
   end