ToLowerCase function can't convert number

I created this code in order to obtain the number related to the data-instrument-id in this html page "https://app.plus500.com/trade/amazon", before finding the data-instrument-id i specified the upper class (I'm not an expert in html). Once I run the code I get back this error :

"selenium.common.exceptions.JavascriptException: Message: javascript error: b.toLowerCase is not a function"

I read on internet that this error comes out because I didn't convert the number I get from the data-instrument-id, but I still can't convert it because I should do it inside the .get_attribute function.

focus on the def get_options if you need to see the website use this username: myrandomcode@gmail.com and this password: MyRandomCode86

don't worry is a dummy account

def get_options():
    opzioni = []
    opzioni_ottenute = WebDriverWait(driver, 20).until(EC.visibility_of_element_located((By.XPATH, "//div["
                                                                                                   "starts-with("
                                                                                                   "@class, "
                                                                                                   "'section-table-body"
                                                                                                   "')]//span[text( "
                                                                                                   ")='Amazon"
                                                                                                   "']//following "
                                                                                                   "::div[ "
                                                                                                   "2]")))
    id_og = opzioni_ottenute.get_attribute((By.CSS_SELECTOR, "data-instrument-id"))
    print(id_og)
    indice = 0
    while indice < 21:
        if (id_og[indice] % 2) != 0:
            opzioni.append(id_og)
            indice = indice + 1
    print(opzioni)