Step 1: Data Button
Go to Setting and Select Mobile Data and search Snapchat app in list and check the button in front of the app, and turn it on.
Step 2 :
Check Date and Time
Go to Setting select General and select Time and Date Setting is proper and your phone is up to date.
Reset Network Setting.
Reset Network Setting is 100% safe, you don’t lose any data or Esim setting, only you need to set up your wifi password again after resetting.
Go to Settings and select General and now go to Reset option here, Properly Select Reset Network Setting and enter your passcode. it will take few seconds and the phone will restart. just go to AppStore and download the snpapchat app, that’s all.