SLD99 - EPSG:5233

WKT

GEOGCS["GCS_SLD99", 
	DATUM["D_Sri_Lanka_Datum_1999", 
		SPHEROID["Everest_Adjustment_1937", 6377276.345, 300.8017]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GCS_SLD99", 
	DATUM["D_Sri_Lanka_Datum_1999", 
		ELLIPSOID["Everest_Adjustment_1937", 6377276.345, 300.8017]], 
	PRIMEM["Greenwich", 0.0], 
	CS[ellipsoidal, 2], 
	AXIS["Latitude (lat)", north, 
		ORDER[1]], 
	AXIS["Longitude (lon)", east, 
		ORDER[2]], 
	ANGLEUNIT["Degree", 0.0174532925199433], 
	ID["EPSG", "5233"]]

Data from @esri/proj-codes

{
  "wkid": 5233,
  "latestWkid": 5233,
  "macro": "PE_GCS_SLD99",
  "name": "GCS_SLD99",
  "wkt": "GEOGCS[\"GCS_SLD99\",DATUM[\"D_Sri_Lanka_Datum_1999\",SPHEROID[\"Everest_Adjustment_1937\",6377276.345,300.8017]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GCS_SLD99\",DATUM[\"D_Sri_Lanka_Datum_1999\",ELLIPSOID[\"Everest_Adjustment_1937\",6377276.345,300.8017]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433],ID[\"EPSG\",\"5233\"]]",
  "description": "SLD99",
  "authority": "EPSG",
  "version": "7.5.9(10.1.0)",
  "deprecated": "no",
  "areaname": "Sri Lanka - onshore",
  "extent": {
    "slat": 5.86,
    "nlat": 9.88,
    "llon": 79.64,
    "rlon": 81.95
  }
}