diff --git a/apps/server/src/api-data/excel/excel.service.ts b/apps/server/src/api-data/excel/excel.service.ts
index 04000b05b..e571302d0 100644
--- a/apps/server/src/api-data/excel/excel.service.ts
+++ b/apps/server/src/api-data/excel/excel.service.ts
@@ -51,7 +51,7 @@ export function generateRundownPreview(options: ImportMap): { rundown: OntimeRun
   }
 
   // clear the data
-  excelData = undefined;
+  excelData = xlsx.utils.book_new();
 
   return { rundown, customFields };
 }
diff --git a/apps/server/src/services/sheet-service/SheetService.ts b/apps/server/src/services/sheet-service/SheetService.ts
index f675e1a1a..edff169e3 100644
--- a/apps/server/src/services/sheet-service/SheetService.ts
+++ b/apps/server/src/services/sheet-service/SheetService.ts
@@ -74,10 +74,11 @@ export function revoke(): ReturnType<typeof hasAuth> {
  */
 export function handleClientSecret(clientSecret: string): ClientSecret {
   const clientSecretObject = JSON.parse(clientSecret);
-  const isValid = validateClientSecret(clientSecretObject);
 
-  if (!isValid) {
-    throw new Error('Client secret invalid');
+  try {
+    validateClientSecret(clientSecretObject);
+  } catch (error) {
+    throw new Error(`Client secret is invalid: ${error}`);
   }
 
   return clientSecretObject;
diff --git a/apps/server/src/services/sheet-service/sheetUtils.ts b/apps/server/src/services/sheet-service/sheetUtils.ts
index 5142446e7..e15110bef 100644
--- a/apps/server/src/services/sheet-service/sheetUtils.ts
+++ b/apps/server/src/services/sheet-service/sheetUtils.ts
@@ -1,7 +1,8 @@
-import { isOntimeBlock, isOntimeEvent, OntimeRundownEntry } from 'ontime-types';
+import { isOntimeBlock, isOntimeEvent, OntimeEvent, OntimeRundownEntry } from 'ontime-types';
 import { millisToString } from 'ontime-utils';
 
 import { sheets_v4 } from '@googleapis/sheets';
+import { isObject } from '../../utils/assert.js';
 
 // we expect client secret file to contain the following keys
 const requiredClientKeys = [
@@ -26,10 +27,21 @@ export type ClientSecret = {
 /**
  * Guard validates a given client secrets file
  * @param clientSecret
- * @returns
+ * @throws
  */
 export function validateClientSecret(clientSecret: object): clientSecret is ClientSecret {
-  return requiredClientKeys.every((key) => Object.keys(clientSecret['installed']).includes(key));
+  if (!('installed' in clientSecret)) {
+    throw new Error('Missing "installed" object');
+  }
+
+  const { installed } = clientSecret;
+  isObject(installed);
+
+  if (requiredClientKeys.every((key) => Object.keys(installed).includes(key))) {
+    return;
+  }
+
+  throw new Error('Missing keys in "installed" object');
 }
 
 /**
@@ -65,18 +77,18 @@ export function getA1Notation(row: number, column: number): string {
  * @param {OntimeRundownEntry} event
  * @param {number} index - index of the event
  * @param {number} worksheetId
- * @param {any} metadata - object with all the cell positions of the title of each attribute
+ * @param {object} metadata - object with all the cell positions of the title of each attribute
  * @returns {sheets_v4.Schema} - list of update requests
  */
 export function cellRequestFromEvent(
   event: OntimeRundownEntry,
   index: number,
   worksheetId: number,
-  metadata,
+  metadata: object,
 ): sheets_v4.Schema$Request {
   const rowData = Object.entries(metadata)
     .filter(([_, value]) => value !== undefined)
-    .sort(([_a, a], [_b, b]) => a['col'] - b['col']) as [string, { col: number; row: number }][];
+    .sort(([_a, a], [_b, b]) => a['col'] - b['col']) as [keyof OntimeEvent | 'blank', { col: number; row: number }][];
 
   const titleCol = rowData[0][1].col;
 
@@ -113,7 +125,7 @@ export function cellRequestFromEvent(
   };
 }
 
-function getCellData(key: string, event: OntimeRundownEntry) {
+function getCellData(key: keyof OntimeEvent | 'blank', event: OntimeRundownEntry) {
   if (isOntimeEvent(event)) {
     if (key === 'blank') {
       return {};
@@ -126,14 +138,13 @@ function getCellData(key: string, event: OntimeRundownEntry) {
       return { userEnteredValue: { stringValue: event.custom[customKey] } };
     }
 
-    const dataType = typeof event[key];
-    if (dataType === 'number') {
+    if (typeof event[key] === 'number') {
       return { userEnteredValue: { stringValue: millisToString(event[key]) } };
     }
-    if (dataType === 'string') {
+    if (typeof event[key] === 'string') {
       return { userEnteredValue: { stringValue: event[key] } };
     }
-    if (dataType === 'boolean') {
+    if (typeof event[key] === 'boolean') {
       return { userEnteredValue: { boolValue: event[key] } };
     }
   }
diff --git a/apps/server/src/utils/__tests__/oscArgParser.test.ts b/apps/server/src/utils/__tests__/oscArgParser.test.ts
index 06fceee41..2293579d5 100644
--- a/apps/server/src/utils/__tests__/oscArgParser.test.ts
+++ b/apps/server/src/utils/__tests__/oscArgParser.test.ts
@@ -15,19 +15,19 @@ describe('test stringToOSCArgs()', () => {
 
   it('empty is nothing', () => {
     const test = undefined;
-    const expected = [];
+    const expected: any[] = [];
     expect(stringToOSCArgs(test)).toStrictEqual(expected);
   });
 
   it('empty is nothing', () => {
     const test = '';
-    const expected = [];
+    const expected: any[] = [];
     expect(stringToOSCArgs(test)).toStrictEqual(expected);
   });
 
   it('1 space is nothing', () => {
     const test = ' ';
-    const expected = [];
+    const expected: any[] = [];
     expect(stringToOSCArgs(test)).toStrictEqual(expected);
   });
 
diff --git a/apps/server/src/utils/__tests__/parser.test.ts b/apps/server/src/utils/__tests__/parser.test.ts
index 779d9e400..651837f18 100644
--- a/apps/server/src/utils/__tests__/parser.test.ts
+++ b/apps/server/src/utils/__tests__/parser.test.ts
@@ -550,7 +550,7 @@ describe('test aliases import', () => {
           pathAndParams: 'testpathAndParams',
         },
       ],
-    } as DatabaseModel;
+    } as unknown as DatabaseModel;
 
     const parsed = parseUrlPresets(testData);
     expect(parsed.length).toBe(1);
@@ -602,7 +602,7 @@ describe('test views import', () => {
         app: 'ontime',
         version: '2.0.0',
       },
-    } as DatabaseModel;
+    } as unknown as DatabaseModel;
     const parsed = parseViewSettings(testData);
     expect(parsed).toStrictEqual(dbModel.viewSettings);
   });