Devices can be enrolled with SimpleMDM by scanning the enrollment QR / QCR code from the website. In some instances, scanning this code with a third party iOS app may result in a blank web page being shown.
In order for enrollment to work properly in iOS, Apple requires that the enrollment URL is visited from within the native Safari web browser app. Many QR scanning apps try to open the URLs in an in-app mini browser.
To enroll by QR, see if the app provides the option to open the link in Safari. If not, either find an app that does or copy the link address and paste it in Safari.