I am trying to enter a new invoice, when I click on new invoice the following error comes up "the transaction you are trying to edit has been deleted."

It's great to see you here today, @AW13. 

The error happens when your recent invoice has been deleted. To help fix this, let's first go to the Audit Log to verify if the transaction was saved or deleted. Please make sure to log in to your QuickBooks Online (QBO) account as an admin before performing the steps below.

1. Go to the Settings (Gear) icon at the upper right.
2. Select Audit Log under Tools. 
3. Click the Filter drop-down. 
4. Select the appropriate User, Date, or Events to narrow the results. 
5. Click Apply.

The screenshot below shows you the last three steps. 

If you've verified that the transaction was deleted, I'd suggest re-entering it. Please use the details by clicking View from the History column as seen in the screenshot below. This ensures you're able to create a new invoice. For detailed steps, go through this article: Audit Log. 

However, if the same issue persists, it could be the browser's cache is full. To troubleshoot the issue, let's first access your QBO account via a private browser. It helps us isolate the issue since it doesn't store data in the cache. Here are the following keyboard shortcuts: 

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

From there, go back to the + New button from the left menu. Then, select Invoice under Customers. If it works, clear the cache of your regular browser. This helps the browser to function effectively. If not, I recommend using other supported browsers. 

To confirm if the new invoice was saved, go to Sales from the left menu. Then, select the Invoices tab and find the transaction. 

When your customer pays the invoice, record the payment by using the Receive Payment feature. This ensures your customer balances are up to date. For more information, check out this article: Record Invoice Payments. 

I'll be right here to help if you need anything else. Have a good day, @AW13.