The ESM has a different legal mechanism for calling for more funds compared to the European Financial Stability Facility.
It is part-paid shares.
All Eurozone member states – including Croatia – are shareholders in the ESM, and they have subscribed to €708.5 billion of capital and paid in €80.6 billion of that. The guarantee fund is the difference – €627.9 billion of subscribed-but-not-called capital.
Member states have an unconditional, irrevocable and several obligation to pay that in upon the ESM’s call – meaning that a member state’s obligation to pay its call is not conditional on other member states meeting their calls.