If messure 24vdc on channel AI0 pin I0+ and Uv with voltmeter is normal to have voltage ,resistance on multimeter is high .When connect current source that is low resistance and messurement while be ok ,you messure current on PLC.
On Siemens manual wiring is ok .
et200sp_ai_8xi_2_4_wire_ba_manual_en-US_en-US.pdf