Marda Welcome to the forum!
StitchBuddy for macOS and StitchBuddy HD for iOS / iPadOS are two different products with their own pricing policies, and therefore separate In-App purchases. If you've purchased StitchBuddy Pro for macOS it won't unlock trial restrictions on your iPad (and vice versa).
Please refer to this overview to learn about the differences of both apps, and you'll find direct links to the respective App Store pages at the bottom: Use these or the App Store app on your device to update manually. If you're struggling with the In-App purchase not being recognized this Knowledge Base article might be helpful. But don't be shy to shout - either here or by mail - if you need further assistance 🙂
Edit: For better visibility I'll move this discussion to "Tips & Tricks" as it's not related to help using this forum.