The URL the customer will be redirected to upon a transaction being unsuccessful or cancelled.
You can set in the 2 ways:
1. Dynamically (CancelURL)
«AlphaHPP» → «Paypage Request Reference» → «Request a Paypage Session»
2. Statically («Cancel URL»)
My Magento 2 extension sets CancelURL in the dynamic way, and your statically set value will be ignored.