There are two scenarios you might occur.
1. The accounts dropdown is restricted to top 20 accounts.
You will have to type the account number or the account name to find the account.
2. You can also check the status of the accounts.
Check Chart of Accounts by clicking Administration --> Bulk Operations --> Bulk List Mgt --> Select Data Mgt on the right --> Click COA. (Please see the below screenshot)
If your company has linked accounts from the ERP system, you have to check your ERP system if the account is set up in the ERP system. We will pull those data into our system.