diff --git a/wuttapos/app.py b/wuttapos/app.py
index a06393e..4e76d98 100644
--- a/wuttapos/app.py
+++ b/wuttapos/app.py
@@ -40,7 +40,7 @@ from rattail.files import resource_path
 import flet as ft
 
 import wuttapos
-from wuttapos.util import get_pos_batch_handler
+from wuttapos.util import get_pos_batch_handler, make_button
 
 
 log = logging.getLogger(__name__)
@@ -77,8 +77,9 @@ def main(page: ft.Page):
         ('terminal', handler.get_terminal_id() or '??'),
     ])
 
-    def send_error_email(traceback):
+    def handle_error(exc_type, exc_value, exc_traceback):
         extra_context = OrderedDict(email_context)
+        traceback = ''.join(format_exception(exc_type, exc_value, exc_traceback)).strip()
 
         try:
             uuid = page.session.get('user_uuid')
@@ -101,14 +102,51 @@ def main(page: ft.Page):
         except:
             log.exception("failed to send error email")
 
+        try:
+            def close_bs(e):
+                bs.open = False
+                bs.update()
+
+            bs = ft.BottomSheet(
+                ft.Container(
+                    ft.Column(
+                        [
+                            ft.Text("Unexpected Error", size=24,
+                                    weight=ft.FontWeight.BOLD),
+                            ft.Divider(),
+                            ft.Text("Please be advised, something unexpected has gone wrong.\n"
+                                    "The state of your transaction may be questionable.\n\n"
+                                    "If possible you should consult the IT administrator.\n"
+                                    "(They may have already received an email about this.)",
+                                    size=20),
+                            ft.Container(
+                                content=make_button("Dismiss", on_click=close_bs,
+                                                    height=80, width=120),
+                                alignment=ft.alignment.center,
+                                expand=1,
+                            ),
+                        ],
+                    ),
+                    bgcolor='yellow',
+                    padding=20,
+                ),
+                open=True,
+            )
+
+            page.overlay.append(bs)
+            page.update()
+
+        except:
+            log.exception("failed to show error bottomsheet")
+
     def sys_exc_hook(exc_type, exc_value, exc_traceback):
-        traceback = ''.join(format_exception(exc_type, exc_value, exc_traceback)).strip()
-        send_error_email(traceback)
+        handle_error_email(exc_type, exc_value, exc_traceback)
         sys.__excepthook__(exc_type, exc_value, exc_traceback)
 
     def thread_exc_hook(args):
-        traceback = ''.join(format_exception(args.exc_type, args.exc_value, args.exc_traceback)).strip()
-        send_error_email(traceback)
+        handle_error(args.exc_type, args.exc_value, args.exc_traceback)
+        # nb. as of python 3.10 could just call threading.__excepthook__ instead
+        # cf. https://docs.python.org/3/library/threading.html#threading.__excepthook__
         orig_thread_hook(args)
 
     # custom exception hook for main process
diff --git a/wuttapos/util.py b/wuttapos/util.py
index ad4fc9f..ef994b3 100644
--- a/wuttapos/util.py
+++ b/wuttapos/util.py
@@ -24,6 +24,8 @@
 WuttaPOS utilities
 """
 
+import flet as ft
+
 
 def get_pos_batch_handler(config):
     """
@@ -34,3 +36,17 @@ def get_pos_batch_handler(config):
     """
     app = config.get_app()
     return app.get_batch_handler('pos', default='rattail.batch.pos:POSBatchHandler')
+
+
+def make_button(text, font_size=24, font_bold=True, font_weight=None, **kwargs):
+    """
+    Generic function for making a Container button.
+    """
+    if not font_weight and font_bold:
+        font_weight = ft.FontWeight.BOLD
+    text = ft.Text(text, size=font_size, weight=font_weight)
+
+    kwargs.setdefault('alignment', ft.alignment.center)
+    kwargs.setdefault('border', ft.border.all(1, 'black'))
+    kwargs.setdefault('border_radius', ft.border_radius.all(5))
+    return ft.Container(content=text, **kwargs)
diff --git a/wuttapos/views/pos.py b/wuttapos/views/pos.py
index a667a28..f16435a 100644
--- a/wuttapos/views/pos.py
+++ b/wuttapos/views/pos.py
@@ -657,8 +657,9 @@ class POSView(WuttaView):
         meta_button_width = meta_button_height * 2
         meta_font_size = tenkey_font_size
 
-        def meta_button(text, on_click=None, bgcolor='blue', data=None):
-            return ft.Container(content=ft.Text(text, size=meta_font_size,
+        def meta_button(text, on_click=None, bgcolor='blue', data=None,
+                        font_size=None):
+            return ft.Container(content=ft.Text(text, size=font_size or meta_font_size,
                                                 weight=ft.FontWeight.BOLD),
                                 height=meta_button_height,
                                 width=meta_button_width,
@@ -696,8 +697,8 @@ class POSView(WuttaView):
                     ft.Row(
                         [
                             meta_button("TODO", bgcolor='blue', on_click=self.not_supported),
-                            meta_button("TODO", bgcolor='blue', on_click=self.not_supported,
-                                        data={'error': True}),
+                            meta_button("(TEST ERROR)", bgcolor='red', on_click=self.not_supported,
+                                        font_size=24, data={'error': True}),
                         ],
                         spacing=0,
                     ),
@@ -872,7 +873,7 @@ class POSView(WuttaView):
 
         # test error handler
         if e.control.data and e.control.data.get('error'):
-            raise ValueError("NOT YET SUPPORTED")
+            raise RuntimeError("NOT YET SUPPORTED")
 
         text = "NOT YET SUPPORTED"
         if not feature and e: