Hi Miho, Neartail uses the fields mapped in the Summary settings page to identify the amount to be passed to the payment option (Stripe, Paypal etc). You have deleted the field that was initially mapped. That's why you are getting the error. Login to Neartail > click on the to open it > Edit page will be displayed > In the Neartail Edit page, click on the form title to select it > click on the gear icon next to the form title > Form settings page will be displayed > click on the configure key fields icon next to the Save button in the bottom right corner > Summary settings page will be displayed > select the "合計金額 / Total Amount" field for the Amount option and click Save. You can then submit a response and test the form.

I click on the gear icon next to the form title, so where is the configure key fields icon?

I went back to the original Google form page and added Neartail amount calculation on again. Why field was not mapped again?

Hi! I can't configure the total amount calculation yet. Could you please help me to do it?

You have deleted the amount field that was mapped. So you must map the new field that you have added in the form for Amount. It appears as if you have zoomed in in your browser. That's why you are not able to see the configure key fields icon and the Save button in the bottom right corner. Please see screenshot below.