Hi there, @UVP.
The message "Please choose a vendor when using an Accounts Payable account as a line item" appears when Account Payable account is chosen on a transaction but the name associated with the account is not a vendor name.
You'll want to use the Liability account for your staff to be able to save the journal entry. I also recommend getting in touch with your accountant for guidance. This way, we'll ensure the accuracy of your accounts after recording this.
Additionally, you can always check our Reports and accounting page and learn some tips and managing your accounting.
You can always get back to me whenever you have other concerns. I'm just a post away. Take care and keep safe!