diff --git a/csaxs_bec/bec_ipython_client/plugins/LamNI/lamni.py b/csaxs_bec/bec_ipython_client/plugins/LamNI/lamni.py
index cf71c76..c1c7f18 100644
--- a/csaxs_bec/bec_ipython_client/plugins/LamNI/lamni.py
+++ b/csaxs_bec/bec_ipython_client/plugins/LamNI/lamni.py
@@ -244,6 +244,13 @@ class LamNI(TomoQueueMixin, LamNIAlignmentMixin, LamNIOpticsMixin, LamniGuiTools
         """Set the web password for the current BEC account."""
         self._webpage_gen.set_web_password(password)
 
+    def force_start_webpage(self) -> None:
+        """Manually force-start the webpage uploader with real upload enabled,
+        bypassing the account-match check. For testing/debugging sessions only
+        (e.g. verifying uploads from the allowed subnet, or verifying the
+        remote server blocks uploads from outside it)."""
+        self._webpage_gen.start(force=True)
+
     def _maybe_reset_params_on_account_change(self) -> None:
         """Offer a tomo-parameter reset when the active account has changed.
 
diff --git a/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/webpage_generator_base.py b/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/webpage_generator_base.py
index 272c3a0..bd6d450 100644
--- a/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/webpage_generator_base.py
+++ b/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/webpage_generator_base.py
@@ -58,6 +58,7 @@ Interactive helpers (optional, in the iPython session):
     flomni._webpage_gen.verbosity = 3          # DEBUG: full JSON per cycle
     flomni._webpage_gen.stop()                 # release lock, stop local server
     flomni._webpage_gen.start()                # restart after stop()
+    flomni._webpage_gen.start(force=True)      # bypass account-match check (testing only)
     flomni._webpage_gen.set_web_password("pw") # set web password for current e-account
 
 Session authentication:
@@ -80,6 +81,13 @@ starts a *local-only* status page on a separate port (default 8081, see
 mismatch_local_port) for local debugging: no singleton lock (so it can never
 block the real session's takeover), no remote upload, no session.htpasswd
 changes. Look for "[local-only: account mismatch]" in the startup log / status().
+
+For testing/debugging sessions that intentionally run under a mismatched
+account, start(force=True) skips this fallback and always takes the real
+path (singleton lock, remote upload, session.htpasswd changes) -- e.g. to
+verify uploads work from the allowed subnet, or to verify the remote
+server's IP whitelist rejects uploads from outside it. See force_start_webpage()
+on the Flomni/LamNI setup classes for the console-facing wrapper.
 """
 
 import datetime
@@ -491,7 +499,7 @@ class WebpageGeneratorBase:
     # Public API
     # ------------------------------------------------------------------
 
-    def start(self) -> None:
+    def start(self, force: bool = False) -> None:
         """Start the generator.
 
         If this session already holds the thread, does nothing.
@@ -499,8 +507,18 @@ class WebpageGeneratorBase:
         is launched that polls every 3 s and takes over as soon as the lock
         goes stale — no blocking, no second call to start() needed.
         Progress messages during the wait are printed at verbosity >= 2 only.
+
+        force=True skips the BEC-account/system-user match check and always
+        takes the real (non-local-only) path: singleton lock, remote upload,
+        session.htpasswd changes — as if the account matched. For manual
+        testing/debugging only (e.g. verifying uploads work from the allowed
+        subnet, or verifying the remote server rejects uploads from outside
+        it) when running under a mismatched account. Logged at warning level
+        since it bypasses a safety check and can affect the shared web page.
         """
-        if not _check_account_match(self._bec):
+        account_match = _check_account_match(self._bec)
+
+        if not force and not account_match:
             if self._thread is not None and self._thread.is_alive():
                 self._log(VERBOSITY_NORMAL, "WebpageGenerator already running in this session.")
                 return
@@ -513,6 +531,12 @@ class WebpageGeneratorBase:
             self._launch(local_only=True)
             return
 
+        if force and not account_match:
+            self._log(VERBOSITY_NORMAL,
+                      "WebpageGenerator: force-starting with real upload despite "
+                      "BEC account / system user mismatch (manual override).",
+                      level="warning")
+
         if self._thread is not None and self._thread.is_alive():
             self._log(VERBOSITY_NORMAL, "WebpageGenerator already running in this session.")
             return
diff --git a/csaxs_bec/bec_ipython_client/plugins/flomni/flomni.py b/csaxs_bec/bec_ipython_client/plugins/flomni/flomni.py
index a4678ec..b8693a1 100644
--- a/csaxs_bec/bec_ipython_client/plugins/flomni/flomni.py
+++ b/csaxs_bec/bec_ipython_client/plugins/flomni/flomni.py
@@ -1659,6 +1659,13 @@ class Flomni(
         """Set the web password for the current BEC account."""
         self._webpage_gen.set_web_password(password)
 
+    def force_start_webpage(self) -> None:
+        """Manually force-start the webpage uploader with real upload enabled,
+        bypassing the account-match check. For testing/debugging sessions only
+        (e.g. verifying uploads from the allowed subnet, or verifying the
+        remote server blocks uploads from outside it)."""
+        self._webpage_gen.start(force=True)
+
     def _maybe_reset_params_on_account_change(self) -> None:
         """Offer a tomo-parameter reset when the active account has changed.