If the voucher related to a Tripsheet is already imported but still throws an error stating that one of the associate bills is not imported in accounts, the issue may be due to the Maintain Bill by Bill flag being enabled. When this flag is checked, the voucher reference will default to New Reference, which can trigger an error if the associated bill is not properly linked.

Resolution:
Uncheck the Maintain Bill by Bill flag in the respective Debit or Credit Accounts to resolve the issue.