Can I save MP3 files to my iTunes Library?

iOS does not allow to save MP3 files directly to your iTunes library within the App. This is a restriction by Apple and we could do nothing about it right now. To add the MP3 files to your iTunes library, you still need to use iTunes to sync them when the device is connected. 

To save MP3 to your iTunes Music library , please follow the steps below:

Step 1: Transfer the MP3 files to your computer. 
You can use one of your Cloud Drives, such as iCloud Drive, Google Drive, Dropbox etc. to do so. 

Step 2: Move the MP3 files into your iTunes playlist.
Start your iTunes on your computer. Find the files on your computer and add them to your iTunes playlist.

Step 3: Sync music with your iPhone/iPad
Hook up your iPhone/iPad with iTunes. Select your device then click Music. Check Sync Music and select the music you would like to add to your device.