SUM function can allow you to add values(numbers or dates) in a table using a calculated or text field but the calculated or text field will be outside the table, not inside the table in an app as you can see in the following link.

▼ SUM Function at Automatic Calculation

https://get.kintone.help/hc/en-us/articles/115001462667-Automatic-Calculation#sum

https://get.kintone.help/hc/en-us/articles/115001462667-Automatic-Calculation#sum

In this case, for "Values" to sum up, please specify the code of a "Number" field, the formula that results in a numerical value, or a number.

For example, to sum up values in the Subtotal fields, whose field codes are "AMT_C" of a table, the formula in a calculated or text field is SUM(AMT_C).