Hi @yashag2255 ,
I have now used Patch to collect data. Formula on the expense header screen "Create" button OnSelect is
Patch(ExpenseReport_2,Defaults(ExpenseReport_2),{'Expense Type': DataCardValue2.Selected ,'Expense Amount': Value(DataCardValue30.Text), Title: DataCardValue1.Text, Name: DataCardValue3.Text, 'Email Address': DataCardValue4.Text, Department: DataCardValue5.Text, Purpose: DataCardValue6.Text, 'Claim Submission Date': DataCardValue7.SelectedDate,Status: "Open"});Set(SelectedReport2, Last(ExpenseReport_2));UpdateContext({Defaults: false, DefaultDate: Today(), DefaultTextValue: "1"});
UpdateContext({Defaults: true, DefaultDate: Today(), DefaultTextValue: ""});
ClearCollect(DefaultRecord, "");
UpdateContext({clearTest_ExpenseHeaderPage:true});UpdateContext({clearTest_ExpenseHeaderPage:false}); Navigate(Test_CreateNewLineItem, None);
Expense Type is a dropdown list, and Expense Amount is a currency value.

When I click on "Create" button, it would bring me to the Expense Detail screen, which has this formula on both "Save and Add New Expense" button and "Save" button.

Patch(ExpenseReport_2,Defaults(ExpenseReport_2), {'Expense Amount': Value(DataCardValue30.Text), 'Expense Type': DataCardValue2.Selected});UpdateContext({Defaults: false, DefaultDate: Today(), DefaultTextValue: "1"});
UpdateContext({Defaults: true, DefaultDate: Today(), DefaultTextValue: ""});
ClearCollect(DefaultRecord, "");
UpdateContext({clearTest_CreateNewLineItem:true});UpdateContext({clearTest_CreateNewLineItem:false});
When I click on Save, nothing is written to SharePoint. When I go back to the Edit mode, I see at the header screen against the Create button that error "ExpenseType: Field Required". At the Details screen, I see against the Save buttons "Title: Field Required". All details have been filled out beforehand though.

All Fields are set as Required in SharePoint and on Powerapps.
(There was twice during my repeated testing that it got written to SharePoint, though the Expense Amount value is not captured. However now, it went back to not being able to write to SharePoint.)
Appreciate your advice. Thank you.