WHEN I TRY TO ADD A NEW CLIENT I GET ERROR CODE 81624

I've got the steps you need to fix the error code when adding a new client in QuickBooks Online (QBO), @sthembiso-mtheth. 

It could be the browser's stored cache is full. This may cause unusual behavior in QBO. That's why you're getting an error code 81624 when adding a new client. 

To help fix this, let's start with accessing your QBO account using an incognito window. It doesn't store data in the cache. Thus, it's a great way to isolate browser-related issues. Here are the keyboard shortcuts depending on the browser you're using: 

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Shift + N
• Microsoft Edge: Ctrl + Shift + P

Once logged in, add your new client again from the Customers tab. If it works, let's clear the cache of your main browser. It removes the browser's stored cache, so it'll function efficiently. However, if the issue persists, you can use another supported browser. 

After that, you'll be able to create sales transactions for your new client. Two of them are invoices and sales receipts. 

Moreover, you can go to the Transaction List of the customer. From there, you can view, edit, print, send, copy, delete, or void transactions. It helps you ensure their balances are up to date. See the screenshot below for your visual reference. For more details, visit this article: Sales Transactions Overview.

I'll be right here to help if you need further assistance. Enjoy the rest of your day, @sthembiso-mtheth.