How to Fix Signature Verification Failed Error 21 when sideloading Magisk

In this video, we will show you the steps to fix the "Signature Verification Failed Error 21 Installation Aborted "when you are sideloading Magisk via custom recovery. Out of all the plausible methods, the easiest way of rooting any custom ROM is by sideloading the Magisk ZIP via the built-in custom recovery that came with the ROM [since those recoveries don’t have the option to directly Install/flash a file, we can only use the ADB Sideload option to flash Magisk]. But since the Magisk is not officially signed by the ROM developers, you will get a Signature Verification Failed Error 21 Installation Aborted prompt. In this regard, many custom recoveries [such as LineageOS Recovery] do give you the option to accept the risk and proceed ahead with the installation of Magisk. However, there are a few other custom recoveries that will straightaway abort the process and wouldn’t allow you to proceed ahead. So in this guide, we will show you the steps to fix this Signature Verification Failed Error 21 when sideloading Magisk so that you could then easily root such ROMs via Magisk.