SIPO is a payment tool of the Czech Post (Česká pošta) that collects regular payments into one summary item: instead of several transfers, you pay one amount.
Main Misunderstanding
🔴 SIPO is a payment method, not a type of payment. Advance payments for services can go through SIPO, but the item "SIPO" in a contract by itself does not say anything about what exactly you are paying for and in what amount.