I have acquired a feautre in the store today "moretracks & formats". After this I reinstalled the Music maker Software (because of other problems). The new feature is no longer available in the software now. Do you know how to reinstall the feature?
. . . . After this I reinstalled the Music maker Software . . . .
Did you download and re-install all the Extra Content for the program - the feature should have been in the available downloads?
Can you select more than 8 tracks in the Project settings? If so then the feature is installed.
Failing the above look in the Store for the feature and it should say acquired, if not log out of the Store, restart Music Maker and log back in to the Store and look again.
Apparently, the program cannot successfully verify the purchase status of the content and/or feature item(s) you purchased through the in-app store. Please note, that your credentials for the store are managed through an option within the program. Possibly, the software is not signed into the store system right now, or it's signed in with an incorrect account. Please start the program, access the "Store" tab on the right-hand side of the screen, and open the drop-down menu from the cog wheel item. Choose the "Log in to Store" option and make sure to sign in with the correct MAGIX user account under which you previously obtained the missing content or feature item(s).
If the purchased content/feature doesn't become available under your "Loops" or "Instruments" section, or in the program's functionality, immediately, please open the drop-down menu for the settings again and tick the option to "Show purchased items". Find the missing item(s) within the full list of availabe items. (You may need to switch between the different categories of e.g. soundpools, instruments and features via the drop-down list.) When your mouse cursor is over the item, you should see that, instead of displaying a price, it will give you the option to either enable/download or add the item to your project right away. (A lot of program feature items don't necessarily require a download/installation process. Owning them through the store will simply unlock access to an advanced feature in the program.)
So essentially what John said. I tend to think that the Music Maker start up screen should have a flashing "Make sure your logged into the store" message.