In reply to nrllhclb:
See here an example:
module des(input logic a, output logic b, inout wire c);
endmodule
interface intf();
logic x;
logic y;
wire z;
//logic z;
endinterface
module top();
intf iface();
des DUT(.a(iface.x), .b(iface.y), .c(iface.z));
endmodule
Replacing the wire in the interface with logic results in the error message:
inout.sv(15): Illegal inout port connection for ‘c’ (3rd connection).