When an end-user has a lot of line items to add to a form grid, especially when the items already exist in a spreadsheet, it would be easier to simply copy the rows of items from a spreadsheet into the grid.
To paste spreadsheet rows into a grid, copy data from a spreadsheet and paste it into the rich text field (drop zone). If the data has the same column layout as the grid, there should be a successful amount of rows in the grid.
Right-click and save the files to your desktop. Import the .json file as a new form. Use the Excel file to test cutting and pasting into the drop zone on the form.