El Hierro height - EPSG:9401

WKT

VERTCS["El_Hierro_height", 
	VDATUM["El_Hierro"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["El_Hierro_height", 
	VDATUM["El_Hierro"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "9401"]]

Data from @esri/proj-codes

{
  "wkid": 9401,
  "latestWkid": 9401,
  "macro": "PE_VCS_EL_HIERRO_HT",
  "name": "El_Hierro_height",
  "wkt": "VERTCS[\"El_Hierro_height\",VDATUM[\"El_Hierro\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"El_Hierro_height\",VDATUM[\"El_Hierro\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"9401\"]]",
  "description": "El Hierro height",
  "authority": "EPSG",
  "version": "9.8.13(12.9.0)",
  "deprecated": "no",
  "areaname": "Spain - Canary Islands - El Hierro",
  "extent": {
    "slat": 27.58,
    "nlat": 27.9,
    "llon": -18.22,
    "rlon": -17.83
  }
}