How to disable Submit button after data submission success

I’d like to set the form’s submit button to disabled after the form has successfully submitted its data. The button should be disabled and not respond to further clicks, so I’m referring to the disabled attribute, not the disabled class. I followed a tute here which disabled the button while “executing” but want it to also be disabled after the data has been successfully submitted so the user cannot resubmit it.
I tried to do it by turning the form’s ‘Success’ event where I already have a notification displayed into an inline event and then running an action: “formssa.btn3.disable(-1)” and also tried “formssa.btn3.disable(true)”. Neither worked.
Any ideas how to do this simple action?

Thank you