Since the iPhone 4s is considered "vintage," many paid software developers have released free versions of their tools for this specific device.
Bypassing the iCloud Activation Lock on an iPhone 4S running iOS 9.3.6 is possible, but truly "free" and functional methods are rare
This happens if you didn't complete the ramdisk upload. Restore the iPhone 4s to iOS 9.3.6 using iTunes (Download the IPSW from IPSW.me, then Shift+Restore). Then re-run Sliver.
Below is a comprehensive guide on the available free methods, their limitations, and the risks involved. 1. Official & Legitimate Free Methods (Recommended)
to put the device into "pwned DFU" mode, allowing you to delete the Sliver Mac