Expense Object is not available in List of Standard Objects in Application Composer

Summary:

Expense Object is not available in List of Standard Objects in Application Composer

Content (please ensure you mask any confidential information):

We have a requirement to validate numerical value stored in one of the fields (standard or DFF) on Expense Line Item with count of Attendees added to Expense Line Items and prevent the user from saving Expense Line Item or submitting the Expense Report, and give a custom message until the values match. Attendee records are not saved until Expense Line Item is saved explicitly by clicking on 'Save' or 'Save and Close' buttons. We tried using partial trigger against updating the Expense amount on the Expense Line Item manually. But, it doesn’t work in case of selecting 'Split Equally'