You need to ensure you have the GL Account Mappings for both Expense Types: Internal and External Expenses.
Pre-Setup ConnectWise Expenses > Step 1: GL Mapping of Expense Types
If the expenses were created before your Mappings were created, then you can refresh the GL Entries via the accounting interface.
Just click into the Unposted Expenses and select Actions > Refresh GL Entries.
Refer to Pre-Setup ConnectWise Expenses > Step 4: Updating GL Entries from Accounting interface