The basic operation appears to be correct. Using your exact parameters in a web browser you can see it works (you need to replace your token)
https://geocode-api.arcgis.com/arcgis/rest/services/World/GeocodeServer/findAddressCandidates?f=pjso...
Response:
{
"spatialReference": {
"wkid": 4326,
"latestWkid": 4326
},
"candidates": [
{
"address": "1600 Pennsylvania Ave NW, Washington, District of Columbia, 20500",
"location": {
"x": -77.036546998208649,
"y": 38.897675107651253
},
"score": 100,
"attributes": {
},
"extent": {
"xmin": -77.037546998208654,
"ymin": 38.896675107651255,
"xmax": -77.035546998208645,
"ymax": 38.89867510765125
}
}
]
}
1. verify your URL is correct?
2. verify you are URL encoding the address string?
3. verify your token is correct?
--jf