Cannot set up Android Management API in fully managed mode using a QR code

For work I am trying to set up multiple OEM Android tablet devices (Rockchip rk3288 / Android 8.1) as fully managed devices using Google's Android Management API.

Following the quickstart steps I can see that after generating an onboarding QR code I should factory reset the device and tap 6 times to scan the QR code.

Unfortunately it seems that these devices were supplied in such a way that the image does not contain the setup application - after factory reset no setup application runs and I can't find setup among the installed apps.

Does anyone know of a way that I can onbaord the devices as Fully Managed using the Android Management API?

Thanks in advance.

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