Foreign suppliers must be set up as not being registered for G.S.T. This makes sure that purchases do not have G.S.T. calculated. Even if the ledger account the purchases are allocated to has G.S.T enabled.
Imported goods incurr a G.S.T. charge when they enter the country. This means G.S.T is paid as a lump sum, rather than per item.
Business Accounts provides a special field in G.S.T. imputation to handle such G.S.T. payments. You need to set up an expense ledger account that is not subject to tax, and with G.S.T. disabled.