When installing the SalesMatik app directly from a link instead of via the App Store, you need to you can get a notification about an Untrusted Enterprise Developer.
To be able to continue the installation, you'll need to "Trust d/nk as a developer" for your iPad / iPhone.
These steps will guide you through the process:
You have entered the direct URL you have received to install the app on your device, for example http://dink.eu/apps/nameofyourcompany
On the screen that opens you clicked on the install-button + 'Install' in the pop-up that appears
At that moment a notification pops-up about an 'Untrusted Enterprise Developer':
Here you can click 'Dismiss'
Click on the 'Settings'-icon on the homepage of your device:
Then choose 'General' - 'Device Management' in the settings menu that has opened:
Click on "d/nk" > "Trust d/nk"
So that a pop-up appears where you can click on 'Trust':