REDNAP height - ESRI:105603

WKT

VERTCS["REDNAP_height", 
	VDATUM["Red_Espanola_de_Nivelacion_de_Alta_Precision"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["REDNAP_height", 
	VDATUM["Red_Espanola_de_Nivelacion_de_Alta_Precision"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["Esri", "105603"]]

Data from @esri/proj-codes

{
  "wkid": 105603,
  "latestWkid": 105603,
  "macro": "PE_VCS_REDNAP",
  "name": "REDNAP_height",
  "wkt": "VERTCS[\"REDNAP_height\",VDATUM[\"Red_Espanola_de_Nivelacion_de_Alta_Precision\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"REDNAP_height\",VDATUM[\"Red_Espanola_de_Nivelacion_de_Alta_Precision\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"Esri\",\"105603\"]]",
  "description": "REDNAP height",
  "authority": "Esri",
  "version": "10.3.1",
  "deprecated": "no",
  "areaname": "Spain - mainland and Balearic Islands onshore",
  "extent": {
    "slat": 35.26,
    "nlat": 43.82,
    "llon": -9.37,
    "rlon": 4.39
  }
}