diff --git a/cmd/server/tests/device_pairing_test.go b/cmd/server/tests/device_pairing_test.go
index bfa1afb3..384af391 100644
--- a/cmd/server/tests/device_pairing_test.go
+++ b/cmd/server/tests/device_pairing_test.go
@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 
 	"github.com/google/uuid"
@@ -91,6 +92,55 @@ func wrongPairingCode(code string) string {
 	return string(rotated)
 }
 
+// pairingFormRequest POSTs urlencoded form data — the Content-Type the
+// browser's htmx forms actually send — with a Bearer token.
+func pairingFormRequest(t *testing.T, setup *TestServerSetup, path, token, body string) (int, map[string]interface{}) {
+	t.Helper()
+	req := httptest.NewRequest("POST", path, strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	if token != "" {
+		req.Header.Set("Authorization", "Bearer "+token)
+	}
+	rec := httptest.NewRecorder()
+	setup.Server.Config.Handler.ServeHTTP(rec, req)
+	var resp map[string]interface{}
+	json.Unmarshal(rec.Body.Bytes(), &resp)
+	return rec.Code, resp
+}
+
+// TestPairingClaimAcceptsBrowserFormEncoding pins the htmx path: the
+// confirm card claims via a urlencoded <form>, so echo v5 routes the
+// Content-Type to the `form:` binder, which maps by `form:` struct tag
+// only. (Regression: PairingCodeRequest shipped with a json-only tag,
+// leaving the code empty and every browser claim failing with 400 —
+// "how did lookup find the device if the code is wrong?") The JSON path
+// stays pinned by the tests above; this covers the form twin.
+func TestPairingClaimAcceptsBrowserFormEncoding(t *testing.T) {
+	setup := setupTestServer(t)
+	identifier := fmt.Sprintf("pairing-form-%s", uuid.New().String())
+
+	reg := registerPairingDevice(t, setup, identifier)
+	code := reg["pairing_code"].(string)
+
+	// Form-encoded lookup (the same call the API-side confirm card makes).
+	status, resp := pairingFormRequest(t, setup, "/api/devices/claim/lookup",
+		setup.RegularToken, "pairing_code="+code)
+	require.Equal(t, http.StatusOK, status, "form-encoded lookup must resolve the live code")
+	assert.Equal(t, "Test Pairing Device", resp["device_name"])
+
+	// Form-encoded claim — exactly what the browser's Pair device
+	// button sends (urlencoded hidden input, not JSON).
+	status, resp = pairingFormRequest(t, setup, "/api/devices/claim",
+		setup.RegularToken, "pairing_code="+code)
+	require.Equal(t, http.StatusOK, status, "form-encoded claim must bind the device")
+	assert.Equal(t, true, resp["approved"])
+
+	// The device's own poll delivers credentials — binding really happened.
+	pollStatus, pollResp := pollRegistrationStatus(t, setup, reg["registration_id"].(string))
+	require.Equal(t, http.StatusOK, pollStatus)
+	assert.Equal(t, "approved", pollResp["status"])
+}
+
 func TestPairingClaimHappyPath(t *testing.T) {
 	setup := setupTestServer(t)
 	identifier := fmt.Sprintf("pairing-happy-%s", uuid.New().String())
diff --git a/internal/handlers/devices.go b/internal/handlers/devices.go
index ffe2d77f..472ed558 100644
--- a/internal/handlers/devices.go
+++ b/internal/handlers/devices.go
@@ -104,7 +104,9 @@ type DeviceApprovalRequest struct {
 // PairingCodeRequest carries the 6-digit code shown on a registering
 // device's screen — the claim credential for the pairing flow.
 type PairingCodeRequest struct {
-	PairingCode string `json:"pairing_code"`
+	// form tag mirrors json: htmx posts urlencoded, the API posts JSON —
+	// echo v5's form binder maps by `form:` tag only (auth.go convention).
+	PairingCode string `form:"pairing_code" json:"pairing_code"`
 }
 
 // PairingLookupResponse describes a live registration without binding it —
@@ -117,7 +119,7 @@ type PairingLookupResponse struct {
 }
 
 type CancelRegistrationRequest struct {
-	RegistrationID string `json:"registration_id" validate:"required"`
+	RegistrationID string `form:"registration_id" json:"registration_id" validate:"required"`
 }
 
 type PendingRegistration struct {