Grid web services are special. The action is POST. It is actually doing a get request. The reason for using POST is that Open API specifications do not allow for a request body.
Below is sample grid for alert.
{
"GRID_TYPE": {
"TYPE": "LIST"
},
"GRID": {
"CURRENT_TAB_NAME": "LST",
"GRID_ID": "2489",
"GRID_NAME": "BSALRT",
"USER_FUNCTION_NAME": "BSALRT"
}, "
DATASPY": {
"DATASPY_ID": "2462"
},
"ADDON_FILTER": {
"ALIAS_NAME": "alertcode",
"OPERATOR": "BEGINS",
"VALUE": "00001"
},
"REQUEST_TYPE": "LIST.HEAD_DATA.STORED"
}