Allow unknown sources from my app

I'm going to do a project for machines that will have a monitor, I'm using an Android tablet, but it shouldn't have access to common actions of a conventional tablet, it should only be for monitoring, so I configured in Devices/Configuration a Device restrictions in kiosk mode single app, it worked as expected but in my app it has a part that has an apk update via wifi, but for some reason when I configure it for kiosk mode single app it messes up the process, I'll show the screens that appear when I don't configure it for kiosk mode single app (the images are in Portuguese, sorry, I'll translate):

1) 

Translation: For your security, the smartphone does not have permission to install unknown apps from this source. You can change this in the settings.
After I click on settings, it redirects to another screen, which will be the next one:

2)

Translation: title = install unknown apps. Allow from this source, and not in front there is the swith to click, after clicking on the swith it opens the pop up to click on update, and this is working correctly.

But as I said at the beginning when I set it to kiosk mode single app these two pop ups do not appear and it is not possible to continue the update, I do not know if it is possible but I thought of two solutions that would be: something that allowed it to appear even in kiosk mode single app and the other that would be ideal that it already gave permission to download in the first pop up, then it has to redirect to settings and after this whole process it updates, so I do not know if it is possible to already grant this permission (I have already configured in Devise restricts applications/Allow installation from unknown sources and also in Apps/Configuration I created a Managed devices and automatically granted all permissions and none of it worked). Thank you for your attention and I will wait, if you have any questions or if you need more details I am at your disposal.