Its the frequency bands they support:
The LG G5 RS988 supports 4 GSM bands, 5 UMTS bands, 10 LTE bands, and 2 CDMA bands (Verizon and Sprint).
RS988
The LG G5 H860 TD-LTE supports 4 GSM bands, 5 UMTS bands, and 15 LTE bands (does not work on Verizon/Sprint).
H860
Click those links to see if they support your carrier.