If you want to call api in minoration mode, you have to pass a cValue parameter at each request.
For instance :
curl -X GET --header "Accept:application/json" 'https://api.test.jackpot-io.com/v1/token?initializationToken=<your-initializationToken>' -k --header "Authorization: Bearer <your-apiKey>"
curl -X GET --header "Accept:application/json" 'https://api.test.jackpot-io.com/v1/offers?cValue=<your-custom-amount>' -k --header "Authorization: Bearer <your-sessionToken>"
curl -X POST --header "Accept:application/json" 'https://api.test.jackpot-io.com/v1/offer/<your-offer-id>/reserve?cValue=<your-custom-amount>' -k --header "Authorization: Bearer <your-sessionToken>"
You will get a voucher worth discountedValue
property, which is cost of purchasing the voucher (decimal number : price with cents).