As old Payments can be w/o start date just set it to now.

master/bt5/vifib_upgrader/SkinTemplateItem/portal_skins/vifib_upgrader/ERP5Site_confirmPlannedPayment.xml

@@ -50,7 +50,7 @@
         </item>
         <item>
             <key> <string>_body</string> </key>
-            <value> <string>context.getPortalObject().portal_catalog.searchAndActivate(method_id=\'confirm\',\n
+            <value> <string>context.getPortalObject().portal_catalog.searchAndActivate(method_id=\'PaymentTransaction_setStartDateAndConfirm\',\n
   method_kw={\'comment\': \'Migrated payment to confirmed state, as this is expected one.\'},\n
   portal_type=\'Payment Transaction\', simulation_state=\'planned\')\n
 \n

master/bt5/vifib_upgrader/SkinTemplateItem/portal_skins/vifib_upgrader/PaymentTransaction_setStartDateAndConfirm.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>Script_magic</string> </key>
+            <value> <int>3</int> </value>
+        </item>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_container</string> </key>
+                                <value> <string>container</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_context</string> </key>
+                                <value> <string>context</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_m_self</string> </key>
+                                <value> <string>script</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>_body</string> </key>
+            <value> <string>import DateTime\n
+assert context.getPortalType() == \'Payment Transaction\'\n
+assert context.getSimulationState() == \'planned\'\n
+\n
+start_date = context.getStartDate()\n
+if start_date is None:\n
+  start_date = context.setStartDate(DateTime.DateTime())\n
+  context.confirm(comment=comment)\n
+</string> </value>
+        </item>
+        <item>
+            <key> <string>_params</string> </key>
+            <value> <string>comment</string> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>PaymentTransaction_setStartDateAndConfirm</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>

master/bt5/vifib_upgrader/bt/revision

-139
+140
\ No newline at end of file