I think you still don't understand what is happening.
When you book into a hotel, most hotels put a " hold" on your credit card as you check in for " insurance "..... using any credit card, nobody is physically taking any money out of your bank, there is no transaction - it's a request to hold funds, in the case you skip checkout and have raided the mini bar or not paid room service - the hotel can decide to change the hold to a withdraw of funds so that the hotel does not loose any money. The customer then owes their bank the credit card debt.... instead of owing the hotel for the missing mini bar / room service that was never paid for - No interest is charged, unless they withdraw from your credit account.
Splitit - is the hotel. All they do is put a temporary hold on funds... for as many months as you select at checkout. Neither Splitit or the credit card bank are using " borrowed funds" to allow the transaction to occur. Splitit are simply using your credit card as equity, while they wait for you to pay the entire amount. There is no interest payable to splitit or the issuing bank as no money is withdrawn. Splitit get the 1.5% according to what I have read, if the merchant is happy to be paid in installments.... splitit are just providing a fail safe mechanism for this to happen, so that the merchant 100% always gets paid - even if the customer stops paying.
For the customer - the purchase is interest free.... If the merchant pays the 1.5% fee, sure maybe they increase the price of everything in the store by 1.5% - go shop somewhere else if you have a better option - but the people using this I think don't have a better, easier option to use.
For the Credit card issuing bank - they simply recieve a hold request on the card - just like they would from a hotel or expensive dinner venue. As the customer pays Splitit the remaining payments, splitit reduce the outstanding hold to match the remaining balance. As I mentioned before, if the customer fails to make payment, then splitit withdraws the remaining balance owed to pay the merchant, and the bank is then owed interest by their customer at whatever rate they charge it at.
For the Retailer - splitit have already said that they will pass on all credit costs + their fee to the merchant, if the merchant decides to ask for up front payment. I dont''t know who is actually getting finance..... it might be the merchant getting finance direct with a provider and splitit is on the side of the transaction, or splitit could be like a broker, or splitit provide their own finance. It's so low risk, the rate would be much better than the big banks - as their is zero risk.
Expand