diff --git a/src/libs/ReportUtils.ts b/src/libs/ReportUtils.ts
index e9c017db43ce..0c2f4f318ce5 100644
--- a/src/libs/ReportUtils.ts
+++ b/src/libs/ReportUtils.ts
@@ -1039,8 +1039,8 @@ function isSettled(reportOrID: OnyxInputOrEntry<Report> | SearchReport | string
 /**
  * Whether the current user is the submitter of the report
  */
-function isCurrentUserSubmitter(reportID: string): boolean {
-    if (!allReports) {
+function isCurrentUserSubmitter(reportID: string | undefined): boolean {
+    if (!allReports || !reportID) {
         return false;
     }
     const report = allReports[`${ONYXKEYS.COLLECTION.REPORT}${reportID}`];
@@ -7379,8 +7379,8 @@ function getWorkspaceChats(policyID: string, accountIDs: number[], reports: Onyx
  *
  * @param policyID - the workspace ID to get all associated reports
  */
-function getAllWorkspaceReports(policyID: string): Array<OnyxEntry<Report>> {
-    return Object.values(allReports ?? {}).filter((report) => (report?.policyID ?? '-1') === policyID);
+function getAllWorkspaceReports(policyID: string | undefined): Array<OnyxEntry<Report>> {
+    return Object.values(allReports ?? {}).filter((report) => report?.policyID === policyID);
 }
 
 /**
diff --git a/src/libs/TransactionUtils/index.ts b/src/libs/TransactionUtils/index.ts
index 8bc1dd7356cb..240ab662f622 100644
--- a/src/libs/TransactionUtils/index.ts
+++ b/src/libs/TransactionUtils/index.ts
@@ -1210,11 +1210,10 @@ function compareDuplicateTransactionFields(
     return {keep, change};
 }
 
-function getTransactionID(threadReportID: string | undefined): string | undefined {
+function getTransactionID(threadReportID?: string): string | undefined {
     if (!threadReportID) {
         return;
     }
-
     const report = allReports?.[`${ONYXKEYS.COLLECTION.REPORT}${threadReportID}`];
     const parentReportAction = ReportUtils.isThread(report) ? ReportActionsUtils.getReportAction(report.parentReportID, report.parentReportActionID) : undefined;
     const IOUTransactionID = ReportActionsUtils.isMoneyRequestAction(parentReportAction) ? ReportActionsUtils.getOriginalMessage(parentReportAction)?.IOUTransactionID : undefined;
diff --git a/src/libs/actions/PersonalDetails.ts b/src/libs/actions/PersonalDetails.ts
index 94a9dc95e846..e0e739b56e86 100644
--- a/src/libs/actions/PersonalDetails.ts
+++ b/src/libs/actions/PersonalDetails.ts
@@ -37,7 +37,7 @@ Onyx.connect({
     key: ONYXKEYS.SESSION,
     callback: (val) => {
         currentUserEmail = val?.email ?? '';
-        currentUserAccountID = val?.accountID ?? -1;
+        currentUserAccountID = val?.accountID ?? CONST.DEFAULT_NUMBER_ID;
     },
 });
 
@@ -121,20 +121,36 @@ function updateDisplayName(firstName: string, lastName: string) {
 
 function updateLegalName(legalFirstName: string, legalLastName: string) {
     const parameters: UpdateLegalNameParams = {legalFirstName, legalLastName};
-
-    API.write(WRITE_COMMANDS.UPDATE_LEGAL_NAME, parameters, {
-        optimisticData: [
-            {
-                onyxMethod: Onyx.METHOD.MERGE,
-                key: ONYXKEYS.PRIVATE_PERSONAL_DETAILS,
-                value: {
-                    legalFirstName,
-                    legalLastName,
+    const optimisticData: OnyxUpdate[] = [
+        {
+            onyxMethod: Onyx.METHOD.MERGE,
+            key: ONYXKEYS.PRIVATE_PERSONAL_DETAILS,
+            value: {
+                legalFirstName,
+                legalLastName,
+            },
+        },
+    ];
+    // In case the user does not have a display name, we will update the display name based on the legal name
+    if (!allPersonalDetails?.[currentUserAccountID]?.firstName && !allPersonalDetails?.[currentUserAccountID]?.lastName) {
+        optimisticData.push({
+            onyxMethod: Onyx.METHOD.MERGE,
+            key: ONYXKEYS.PERSONAL_DETAILS_LIST,
+            value: {
+                [currentUserAccountID]: {
+                    displayName: PersonalDetailsUtils.createDisplayName(currentUserEmail ?? '', {
+                        firstName: legalFirstName,
+                        lastName: legalLastName,
+                    }),
                 },
+                firstName: legalFirstName,
+                lastName: legalLastName,
             },
-        ],
+        });
+    }
+    API.write(WRITE_COMMANDS.UPDATE_LEGAL_NAME, parameters, {
+        optimisticData,
     });
-
     Navigation.goBack();
 }
 
diff --git a/src/pages/home/HeaderView.tsx b/src/pages/home/HeaderView.tsx
index cf7e2adfccd0..8f1933b076f0 100644
--- a/src/pages/home/HeaderView.tsx
+++ b/src/pages/home/HeaderView.tsx
@@ -70,9 +70,11 @@ function HeaderView({report, parentReportAction, reportID, onNavigationMenuButto
     const {isSmallScreenWidth} = useResponsiveLayout();
     const route = useRoute();
     const [isDeleteTaskConfirmModalVisible, setIsDeleteTaskConfirmModalVisible] = React.useState(false);
-    const [invoiceReceiverPolicy] = useOnyx(`${ONYXKEYS.COLLECTION.POLICY}${report?.invoiceReceiver && 'policyID' in report.invoiceReceiver ? report.invoiceReceiver.policyID : -1}`);
+    const [invoiceReceiverPolicy] = useOnyx(
+        `${ONYXKEYS.COLLECTION.POLICY}${report?.invoiceReceiver && 'policyID' in report.invoiceReceiver ? report.invoiceReceiver.policyID : CONST.DEFAULT_NUMBER_ID}`,
+    );
     // eslint-disable-next-line @typescript-eslint/prefer-nullish-coalescing
-    const [parentReport] = useOnyx(`${ONYXKEYS.COLLECTION.REPORT}${report?.parentReportID || report?.reportID || '-1'}`);
+    const [parentReport] = useOnyx(`${ONYXKEYS.COLLECTION.REPORT}${report?.parentReportID || report?.reportID}`);
     const policy = usePolicy(report?.policyID);
     const [personalDetails] = useOnyx(ONYXKEYS.PERSONAL_DETAILS_LIST);
 
@@ -100,7 +102,7 @@ function HeaderView({report, parentReportAction, reportID, onNavigationMenuButto
     const reportDescription = Parser.htmlToText(ReportUtils.getReportDescription(report));
     const policyName = ReportUtils.getPolicyName(report, true);
     const policyDescription = ReportUtils.getPolicyDescriptionText(policy);
-    const isPersonalExpenseChat = isPolicyExpenseChat && ReportUtils.isCurrentUserSubmitter(report?.reportID ?? '');
+    const isPersonalExpenseChat = isPolicyExpenseChat && ReportUtils.isCurrentUserSubmitter(report?.reportID);
     const shouldShowSubtitle = () => {
         if (!subtitle) {
             return false;
@@ -258,7 +260,7 @@ function HeaderView({report, parentReportAction, reportID, onNavigationMenuButto
                                         <PressableWithoutFeedback
                                             onPress={() => {
                                                 if (ReportUtils.canEditPolicyDescription(policy)) {
-                                                    Navigation.navigate(ROUTES.WORKSPACE_PROFILE_DESCRIPTION.getRoute(report.policyID ?? '-1'));
+                                                    Navigation.navigate(ROUTES.WORKSPACE_PROFILE_DESCRIPTION.getRoute(`${report.policyID ?? CONST.DEFAULT_NUMBER_ID}`));
                                                     return;
                                                 }
                                                 Navigation.navigate(ROUTES.REPORT_WITH_ID_DETAILS.getRoute(reportID, Navigation.getReportRHPActiveRoute()));