Form is not getting submitted

I have a form as follows:

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I have a custom action to get user_plan . But user plan varies depending on user_sub . after user tells subs , I will display options thru buttons so user can select one of them. The issue is that if ther is only one button instead of asking him to choose I used SlotSet(user_plan,plans[0]). Exactly: return [SlotSet("user_plan",plans[0]) , FollowupAction("action_ask_cancel_form_user_sub")]

But it doesn’t proceed to next action.

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Here it never does the action utter_confirm when i use slotset . but when I use buttons if does move to utter_confirm . Any suggestion why its happening ?