Penalty clauses in financial contracts are permissible, apart from contracts in which the original commitment is in the form of credit (debt). It is not permissible, for example, to stipulate that the one who buys goods by instalment must pay something additional to the price if he delays payment, because this additional cost is in addition to the debt he owes, and that is Riba.

If the marketing service asked about is based on the customer or purchaser subscribing to something, meaning that he pays a sum of money in return for getting some discount or reduction in prices of goods or services that the seller is offering, then this is a haram transaction. If the transaction is haram, then it is also haram for you to tell people about it or to help people deal with it. For more information, please see the long answer.