How to do a functional + and - for product quantity

[Rose_van_Zijl (R)]

Thank you for sharing @Waldo . I followed the steps but it is not working for me yet. Can someone spot my mistake?

https://preview.webflow.com/preview/bureaurose?utm_medium=preview_link&utm_source=designer&utm_content=bureaurose&preview=e2627b112144588a0550d70ff3263c8a&pageId=64232d4429051a207bd59292&itemId=64233064459cd7400cec3644&workflow=preview

Thanks in advance!