Facebook/Pinterest Login fail through Safari

Hey, I am from Germany, if thats of any relevance for my here described problem!

- I have the Facebook and Pinterest App on my iPhone

- I use Pinterest with my Facebook login details

- Pinterest App always was running smoothly until i logged myself out on my iPhone unwillingly (or stupidity)

- I am still logged in in Safari on my other devices like iMac and I haven't changed my Password either

- Only on my iPhone I can't log myself in anymore. Whenever I try to log myself in over the app and press the Facebook button, Safari opens a tab Facebook.com,

i then enter my Email and Password from Facebook, and nothing happens, the page is refreshed. On Facebook I get a notification saying "someone tried to login with an unknown browser..." I than tell Facebook "YES THAT WAS ME, please save browser" but this notification appears again again again and again!!!

I already deleted Facebook and Pinterest from my iPhone, I deleted the whole Facebook account from my iPhone settings as well!

- I tried to log myself in on an Android phone, which worked perfectly. So my guess that there is a problem with Safari connecting with Facebook ... But I have no idea anymore what I could change in the settings or anywhere so i could login again on Pinterest!

Please help!!!

And yes I know... probably not the most important problem in the world... but still important to me to get back in on Pinterest on my iPhone!

Thank you!!!