Have you read the NOTE under the icons of VISA, MasterCard and Liqpay when selecting the above payment method?
Important! This merchant only for clients from EASTERN EUROPE and CIS. Clients from Western EU should use another merchant (FreeKassa).
InterKassa is linked to Liqpay, correct. InterKassa merchant is for users from the Eastern Europe (including YOU).
FreeKassa is the main merchant for users from Western Europe and they operate through OOOPAY.
I don't understand, if you paid via InterKassa, you would have to be forwarded to Liqpay payment system.
If you were forwarded to OOOPAY, then you paid through FreeKassa, and this is not the option for you.