When creating a new invoice, you have options for how to look up a client. One option is to search by Client ID. When you reset your default options though, this may have reverted to searching by Client Name.
To search for a client by Client ID when adding a new Invoice:
1. Select Tools > Options from the menu bar 2. Select the records tab 3. Select General on the left 4. On the right, move the Client ID to the top spot using the arrows 5. Click Apply > OK