How to add new ledger / party details?

Yes it is possible, you have an option to add new ledgers here in livekeeping.

Go to parties tab > Click on + tab at bottom right corner > Enter ledger name, select their group (sundry creditor / sundry debtor) > other details > submit it by clicking on create ledger.

Once you have added the ledgers (sundry creditor/ sundry debtors) you can create these entries for them after the next syncing.