I cannot select the products or services when I want to create an invoice, that is the list of created inventory is not showing under products / services,

I'm here to get this issue sorted out, @likhon-fnb-gmail. 

There are times that the browser is full of frequently accessed page resources. It may cause unusual behavior in the program. That's why you're unable to select the products or services when creating an invoice. 

I'd first suggest signing in to your QuickBooks Online (QBO) account via an incognito window. It doesn't store data in the cache, so it's a great way to isolate browser-related issues. Here are the keyboard shortcuts: 

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

From there, select a product or service on the Invoice page again (see the screenshot below). If it works, let's clear your regular browser's cache to have a clean slate, so it'll function efficiently. Otherwise, use other supported web engines to help resolve this.

Once done, I recommend running reports to see your sales and inventory status in QBO. 

When your customer pays the invoice, let's go to the + New menu and select Receive Payment to record it. This way, we can ensure their balances are up to date in the program.

If you have follow-up concerns regarding inventory and invoices in QBO or other inquires, please let me know. I'll be around to help. Keep safe.