Does the PLN 50 amount from the InPost voucher have to be spent in a single purchase? What is the minimum purchase value to use the voucher?

Yes. The InPost voucher is single-use. If the purchase value is less than PLN 59, the voucher cannot be used. If the purchase exceeds PLN 59, the voucher can be applied to receive a PLN 50 discount, and the customer must pay the remaining balance.