Unfortunately, I don’t have a solution for your issue if you don’t have a private key backup …
Here is an old developer post with explanation what probably happen:
Can I ask if you replaced Iphone and did you restored applications from icloud/itunes backup? This is often the case because kechain data are not backuped by default by Apple backups. This causes you have application with some information like address, but your keychain data is not complete (and this is place where private key is stored). When app trying get private key it’s incorrect and that’s why you are unable to export private key or send any transaction.