It looks like you're trying to get working on an older device (likely an iPhone, iPad, or iPod touch running iOS 9 or 10, since 1.5.7 was released around 2015–2016).
: Sign back into your original device. GarageBand will now appear in your "Purchased" section with the cloud icon, allowing you to download the compatible version. Troubleshooting "Does Not Work" Issues garageband ios 157 download work
The older version will lack some modern features—such as multi-window support or newer synth presets—found in the latest updates. It looks like you're trying to get working