Hi Shubha.
A local test for this shows either 'add to cart' & 'checkout' buttons or the 'submit' button in the USS-UI.
How do you (and can I) get the 'submit' and the 'save' button shown together?
Is that some customization you have in place?
As to the triggering of the 'onSubmit' js-function, it gets triggered on the 'add to cart' the 'checkout' and the 'submit' on my local environment. (which might be ootb behavior).
Please advise. Thanks in advance and kind regards, Louis.