Step 01. Make sure to install Siri shortcut first. Please install it from here.
Step 02. Now Open Apple Shortcuts category
Step 03. Tap Install button to install
Step 04. Allow untrusted Shortcuts error
Step 05. Open Shortcuts --> Go to Gallery
Hurray!!! Install any default shortcut. Then you will have the option to allow Allow untrusted Shortcuts
Step 01. Launch your device’s “Settings” application.
Step 02. Tap “Shortcuts.”
Step 03. Tap to enable “Allow Untrusted Shortcuts” slider
Step 04. Read the disclaimer and tap “Allow”
Step 05. When prompted, enter your passcode.
Hurray!!! Now free to install third-party shortcuts on your iPhone or iPad.