If iCloud Keychain is on, but Safari won't save or autofill account or credit card information
On iPhone, iPad, or iPod touch with iOS 9 or later:
- Tap Settings > Safari > AutoFill.
- For account names and passwords, check that Names and Passwords is on. For credit card information,* check that Credit Cards is turned on.
- Open Safari. If the navigation bar in Safari is black or dark instead of white or light gray, turn off Private Browsing. Safari doesn't save account names and passwords when Private Browsing is on.
https://support.apple.com/en-us/HT203783
Turn Private Browsing on or off on your iPhone, iPad, or iPod touch
https://support.apple.com/en-us/HT203036