diff --git a/src/slic3r/GUI/ConnectPrinter.cpp b/src/slic3r/GUI/ConnectPrinter.cpp
index 5d7bf67e03..c69e81f650 100644
--- a/src/slic3r/GUI/ConnectPrinter.cpp
+++ b/src/slic3r/GUI/ConnectPrinter.cpp
@@ -14,6 +14,7 @@
 #include <string>
 #include "slic3r/GUI/wxExtensions.hpp"
 #include "libslic3r/AppConfig.hpp"
+#include "IPrinterAgent.hpp"
 
 #include "DeviceCore/DevManager.h"
 
@@ -169,14 +170,16 @@ void ConnectPrinterDialog::on_input_enter(wxCommandEvent& evt)
 void ConnectPrinterDialog::on_button_confirm(wxCommandEvent &event)
 {
     wxString code = m_textCtrl_code->GetTextCtrl()->GetValue();
-    if (code.empty())
-        code = "88888888";
+    // Validate only what the user typed; the no-key sentinel is applied afterwards (it contains
+    // non-alphanumeric characters, so it must not go through this check).
     for (char c : code) {
         if (!(('0' <= c && c <= '9') || ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z'))) {
             show_error(this, _L("Invalid input"));
             return;
         }
     }
+    if (code.empty())
+        code = NO_API_KEY_SENTINEL;
     if (m_obj) {
         m_obj->set_access_code(code.ToStdString());
     }
diff --git a/src/slic3r/GUI/DeviceManager.cpp b/src/slic3r/GUI/DeviceManager.cpp
index 30e7282c0e..e6e483a3e6 100644
--- a/src/slic3r/GUI/DeviceManager.cpp
+++ b/src/slic3r/GUI/DeviceManager.cpp
@@ -2681,7 +2681,8 @@ int MachineObject::connect()
 {
     if (get_dev_ip().empty()) return -1;
     std::string username = m_agent ? m_agent->default_lan_username() : std::string();
-    std::string password = get_access_code();
+    // The stored access code may be the "no API key" sentinel; agents expect an empty credential.
+    std::string password = normalize_access_code(get_access_code());
 
     std::string port;
     std::string input = get_dev_ip();
diff --git a/src/slic3r/GUI/GUI_App.cpp b/src/slic3r/GUI/GUI_App.cpp
index 11cde7e5f2..45be004c00 100644
--- a/src/slic3r/GUI/GUI_App.cpp
+++ b/src/slic3r/GUI/GUI_App.cpp
@@ -4263,7 +4263,7 @@ void GUI_App::select_machine(const std::string& agent_id)
         auto access_code = preset.config.opt_string("printhost_apikey");
         // Orca expect non empty access code
         if (access_code.empty()) {
-            access_code = "88888888";
+            access_code = NO_API_KEY_SENTINEL;
         }
 
         existing = m_device_manager->insert_local_device(
diff --git a/src/slic3r/GUI/ReleaseNote.cpp b/src/slic3r/GUI/ReleaseNote.cpp
index b200473e08..869c05f47c 100644
--- a/src/slic3r/GUI/ReleaseNote.cpp
+++ b/src/slic3r/GUI/ReleaseNote.cpp
@@ -2,6 +2,7 @@
 #include "I18N.hpp"
 
 #include "bambu_networking.hpp"
+#include "IPrinterAgent.hpp"
 #include "libslic3r/Utils.hpp"
 #include "GUI.hpp"
 #include "GUI_App.hpp"
@@ -1903,7 +1904,7 @@ void InputIpAddressDialog::on_ok(wxMouseEvent& evt)
     std::string str_ip = m_input_ip->GetTextCtrl()->GetValue().ToStdString();
     std::string str_access_code = m_input_access_code->GetTextCtrl()->GetValue().ToStdString();
     if (str_access_code.empty())
-        str_access_code = "88888888";
+        str_access_code = NO_API_KEY_SENTINEL;
     std::string str_name = m_input_printer_name->GetTextCtrl()->GetValue().Strip(wxString::both).ToStdString();
     // Serial number should not contain lower case letters, and bambu_network plugin crashes
     // if user entered the wrong serial number, so we call `Upper()` here.
@@ -1950,7 +1951,7 @@ void InputIpAddressDialog::on_send_retry()
     wxString ip              = m_input_ip->GetTextCtrl()->GetValue();
     wxString str_access_code = m_input_access_code->GetTextCtrl()->GetValue();
     if (str_access_code.IsEmpty())
-        str_access_code = "88888888";
+        str_access_code = NO_API_KEY_SENTINEL;
 
     // check support function
     if (!m_obj) return;
diff --git a/src/slic3r/Utils/IPrinterAgent.hpp b/src/slic3r/Utils/IPrinterAgent.hpp
index 07ce9af33d..98bd8986af 100644
--- a/src/slic3r/Utils/IPrinterAgent.hpp
+++ b/src/slic3r/Utils/IPrinterAgent.hpp
@@ -45,6 +45,17 @@ struct PrinterConnectionParams
     std::string ca_file;
 };
 
+// Sentinel stored as a LAN device's access code when the user has not supplied one, so the device
+// stays registered (has_access_right() is !access_code.empty()). It is not a real credential: every
+// printer agent must translate it back to an empty string before using/sending it on the wire.
+inline constexpr const char* NO_API_KEY_SENTINEL = "*_{NO_API_KEY}_*";
+
+// Returns an empty string when `code` is the "no API key" sentinel, otherwise `code` unchanged.
+inline std::string normalize_access_code(const std::string& code)
+{
+    return code == NO_API_KEY_SENTINEL ? std::string() : code;
+}
+
 /**
  * FilamentSyncMode - Modes for filament data synchronization.
  *
diff --git a/src/slic3r/Utils/MoonrakerPrinterAgent.cpp b/src/slic3r/Utils/MoonrakerPrinterAgent.cpp
index 32fff18342..30c380589a 100644
--- a/src/slic3r/Utils/MoonrakerPrinterAgent.cpp
+++ b/src/slic3r/Utils/MoonrakerPrinterAgent.cpp
@@ -2338,7 +2338,7 @@ void MoonrakerPrinterAgent::announce_printhost_device()
     const std::string model_id = device_info.model_id;
 
     if (auto* app_config = GUI::wxGetApp().app_config) {
-        const std::string access_code = device_info.api_key.empty() ? "88888888" : device_info.api_key;
+        const std::string access_code = device_info.api_key.empty() ? NO_API_KEY_SENTINEL : device_info.api_key;
         app_config->set_str("access_code", device_info.dev_id, access_code);
     }