This error message is generally associated with the name already existing in the file, such as a vendor or employee. Or when you import data from QuickBooks Desktop or turning payroll adding employees in QuickBooks Online that cause duplicates names.
We can change the display name, so it will show in the Supplier's list. I'll guide you how:
Sign in to your QuickBooks Online company file.
Select Expenses, then Suppliers.
Choose the name of the duplicate supplier.
Select Edit (Note: Select Sales and then Customers if you are doing this to check for duplicates in your customer list).
Change the Display name.
Click Save and close.
Also, we can use a private browser to open your account and see if they show up. If the cache becomes too full of older stored data, it can potentially cause viewing and performance errors in QuickBooks Online.
Please use these keyboard shortcuts depending on the browser you're using:
Google Chrome: press Ctrl + Shift + N
Mozilla Firefox: press Ctrl + Shift + P
Microsoft Edge: press Ctrl + Shift + P
Safari: press Command + Shift +N
If the supplier list shows up, let's switch back to the regular browser and clear its cache & historical data. This helps to restore the default setup of the browser.
In case private browsing doesn't work, use another supported browser to get the best and most secure experience with the program.
I've included these articles that will guide you in managing your transactions from the suppliers and how to organize your list in QuickBooks: