Is the fast considered valid if gargling solution goes down the throat, with doubt as to whether it reached the stomach, during a Ramadan daytime?

If gargling is done at the outer part of the mouth out of necessity, it is similar to rinsing the mouth. If any of it precedes to the throat unintentionally and you are unable to return it, your fast is valid, because the mouth is considered like the outer part of the body. However, if it is confirmed that the solution reached the throat, it is preferable to make up that day to avoid the اختلاف (difference of opinion) among scholars.