1) Please, increase the Max input vars limit to 4000 and try again after that.
2) Provide temporary wp-admin and FTP access, so we can take a closer look and help.
3) Provide server error logs.
4) Make sure that you added Valid OAuth redirect URI. For example – https://gyazo.com/211fb3da2fc61a78f4c1cb9d929daa2e Provide us with screenshots of your settings via The Private Content area. Use Gayzo or Lightshot screenshot tools to make and share screenshots.
