While applying a payment, the customer was not found. I checked inactive customers-not there.All history is gone. Reports for different FY's do not include this customer

Welcome to the community, Summer.

Let me share some information about your inquiry on why you can’t find your customer in your QuickBooks Online (QBO) account. 

If you cannot find your customer, I recommend checking your Audit Log in your account by clicking on the Gear icon above. In that way, you can view the changes made to your account and who made the changes. 

Furthermore, let’s perform troubleshooting steps to fix this matter to get rid of this situation. Start by logging in to your QuickBooks Online account using a private or incognito browser.  

You can use these keyboard shortcuts below:

1. Google Chrome: Ctrl + Shift + N
2. Safari 11 or newer: ⌘ + Shift + N
3. Mozilla Firefox: Ctrl + Shift + P
4. Microsoft Edge: Ctrl + Shift + N

From there, check if you can already see your customer and can add payments. If it works, go back to your regular browser and clear its cache for a seamless browsing experience.

In addition, if you're interested in learning more about closing the fiscal year and preparing for the new one in QBO, I suggest taking a look at this article: A year-end guide for QuickBooks Online.

Please let me know in the comments below if there is anything else I can help you with finding your customer in your QBO. I’ll be here to assist you at any time. Have a great day ahead!