how do i insert geometry POINT type data in postgis database ? with asp.net back-end service

Question

I develope geometry survice in asp.net. but i have a problem input my geometry point type data in postgis.

In repository.cs files ..

public async Task<DataList<Data<string>>> Create(BattlespaceData battlespacedata) {
return await Task.Run(async () => {
await Task.Delay(0);

Data<string> par = new Data<string>();

par["pk"] = battlespacedata.pk.ToString();
....
par["coord_lat"] = battlespace.coord_lat.ToString(); // latitude
par["coord_lon"] = battlespace.coord.lon.Tostring(); // longitude

par["a"] = "ST_GeomFromText('POINT(" + battlespace.coord_lat.ToString() + " " + battlespace.coord_lon.ToString() + ")', 4326)";

...

await NpgSqlHelper.SqlExecute(@"
insert into database1 (
battlespacePK,
coord_lat,
coord_lon,
coord
)
VALUES (
@pk,
@coord_lat::float,
@coord_lon::float,
@a::geometry
)

...

but error occurs "XX000: parse error - invaild geometry" help me plz....