@martin-smith3979 Just go into the in-app shop and select the category (instrument/Soundpools) and click on the coupon counter at the bottom. Then select the instruments and Soundpools you are interested in.
@martin-smith3979 You very likely updated from version 2020 to version 2021 (this means it was an upgrade instead of an update). Your coupons are only vaild in version 2020. Uninstall Music Maker and reinstall version 2020. Then you can use your coupons. After that you can update to version 2021 or you can leave version 2020 on your computer and install version 2021 in a different location to use both version in parallel. This works fine and I am doing the same on my computer.
MM Premium 2021, aka version 29, as the first 64 bit release of MM, is viewed by Magix as a "new" program. As such, users wishing to upgrade from MM 2020 to MM 2021 (to retain the full functionality of the variant they previously had) must pay the upgrade price. If you merely update from MM 2020 to MM 2021 without paying, what you then have is the Free variant of MM 2021. This variant is limited to a maximum of 8 tracks, and has no capability to use VSTs or VSTis, amongst other differences.