Great question — answering as the UphillTech team:
If you are trying to sell something for your app itself which it appears you are not doing, would be violating rule 11.2: Apps utilizing a system other than the In-App Purchase API (IAP) to purchase content, functionality, or services in an App will be rejected There is no specific rule against leading to purchase something, unless it is mandatory for your app. There is definitely no rule against putting links into your app, I have apps that have links that lead to websites. You should be fine.
Full answer by Wyetro: https://stackoverflow.stackexchange.com/a/25073291 (CC BY-SA 4.0).
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