I'm trying to get the XPATH for Code Generator field form (Facebook) in order to fill it (of course before I need to put a code with "numbers").
In Chrome console when I get the XPATH I get:

//*[@id="approvals_code"]

And then in my test I put:

elem = driver.find_element_by_xpath("//*[@id='approvals_code']")
if elem: elem.send_keys("numbers")
        elem.send_keys(Keys.ENTER)

With those I get:

StaleElementReferenceException: Message: stale element reference: element is not attached to the page document

What means wrong field name. Does anyone know how to properly get a XPATH?
This error usually comes if element is not present in the DOM. 
Or may be element is in iframe.
Python selenium test - Facebook code generator XPATH