On premises API for web service Custom Connector - 404

[CamSims]

I have a web service installed on a server where I can pull API data via XXX.XXX.com/REST/...

It is limited to on premises access and I'm able to use the API via Postman so long as I'm on the corporate wifi but not when off.

I'm trying to create a custom PowerApps connector which utilizes the API. I've installed the On-Premises data gateway onto my server but not sure what I need to configure. 

My connector settings are:

1. General
   1. Connect via on-premises data gateway - Checked
   2. Scheme - HTTP
   3. Host - xxx.xxx.com
   4. Base URL - /REST/
2. Security
   1. Windows Authentication
3. Definition - Configured for API
4. Test
   1. Selected connection - Gateway connection
      1. Connection Settings:
         1. Authentication Type: Windows
         2. Username/Password: local admin account
         3. Choose a gateway: API Gateway

Results:

Status - (404)

Headers
{
"strict-transport-security": "max-age=31536000; includeSubDomains;,max-age=31536000; includeSubDomains",
"x-content-type-options": "nosniff,nosniff",
"date": "Thu, 05 Sep 2019 20:55:47 GMT",
"x-frame-options": "SAMEORIGIN,DENY",
"content-type": "application/json; charset=utf-8",
"x-ms-request-id": "82355ed7-9af3-4540-84ba-b095-c70d0431",
"cache-control": "private,no-store",
"content-length": "527"
}

Body

{
"Status": 404,
"URL": "/rest/server/authenticationtokens",
"Method": "POST",
"Exception": {
"Name": "NotFoundException",
"Message": "Exception of type 'MFWS.NotFoundException' was thrown."
},
"Stack": "Error reference ID: ea3ac03b-72c5-40a3-9583-6cc867373058",
"Message": "Exception of type 'MFWS.NotFoundException' was thrown.\r\nclientRequestId: 82355ed7-9af3-4540-84ba-b095-c70d0431",
"IsLoggedToVault": false,
"IsLoggedToApplication": false,
"ExceptionName": "NotFoundException"
}

[v-monli-msft]

Hi @CamSims ,

Did you follow steps in below documentation correctly?

https://powerapps.microsoft.com/en-us/blog/on-premise-apis/

Regards,

Mona

[CamSims]

I have. With the exception of creating a web application in VS since I already have a platform running the api (M-Files). 

Do I need to create a separate application in VS?