SBI Unipay works on BBPS, it's instant settlement. Although, it's associated with multiple failures as well.
If you are going to use it, then don't pay huge amount in a single transaction. In case, if the transaction gets failed. There is no dedicated customer support, your only option is to wait 5-7 working days for the refund.
Other portals which are similar to sbi unipay also have this issue.