Why does logic apps retrieve Content-Type must be application/x-www-form-urlencoded if it is passed?

Question

I'm developing a Logic app that should call a specific API one time for a day to retrieve the response (a token) and on the next steps (not already written) it will contact another API and finally it will store the result on a Google spreadsheet. The problem is on the first call, reading the documentation of MailUp I must send a call to an URL to retrieve the token using username e password authentication ( https://help.mailup.com/display/mailupapi/Authenticating+with+OAuth+v2 ) but it doesn't work! Can someone help me?

{
    "definition": {
        "$schema": "https://schema.management.azure.com/providers/Microsoft.Logic/schemas/2016-06-01/workflowdefinition.json#",
        "actions": {
            "HTTP": {
                "inputs": {
                    "headers": {
                        "Authorization": "BASE64_ENCODED_CLIENTCREDENTIALS",
                        "Content-Type": "application/x-www-form-urlencoded"
                    },
                    "method": "POST",
                    "queries": {
                        "grant_type": "password",
                        "password": "password",
                        "username": "username"
                    },
                    "uri": "https://services.mailup.com/Authorization/OAuth/Token"
                },
                "runAfter": {
                    "Initialize_variable": [
                        "Succeeded"
                    ]
                },
                "type": "Http"
            },
            "Initialize_variable": {
                "inputs": {
                    "variables": [
                        {
                            "name": "responseBody",
                            "type": "String",
                            "value": ""
                        }
                    ]
                },
                "runAfter": {},
                "type": "InitializeVariable"
            },
                "type": "ApiConnection"
            },
            "Set_variable": {
                "inputs": {
                    "name": "responseBody",
                    "value": "@{body('HTTP')}"
                },
                "runAfter": {
                    "HTTP": [
                        "Succeeded"
                    ]
                },
                "type": "SetVariable"
            }
        },
        "contentVersion": "1.0.0.0",
        "outputs": {},
        "parameters": {
            "$connections": {
                "defaultValue": {},
                "type": "Object"
            }
        },
        "triggers": {
            "Recurrence": {
                "evaluatedRecurrence": {
                    "frequency": "Day",
                    "interval": 1
                },
                "recurrence": {
                    "frequency": "Day",
                    "interval": 1
                },
                "type": "Recurrence"
            }
        }
    },
    "parameters": {
        "$connections": {
            "value": {
            }
        }
    }
}

Answer 1

Due to access issues, I will not be able to use https://help.mailup.com/display/mailupapi/Authenticating+with+OAuth+v2 here but I will use https://login.microsoft.com/{tenant_id}/oauth2/token to generate bearer token in the same way you are trying to generate them in logic app.

Try to structure the body in the following format like use '&' instead of 'comma' in your case. Use clientId and client_password too along with the username and password. Here I am taking below inputs to generate token:

URL https://login.microsoft.com/{tenant_id}/oauth2/token

Headers Content-Type: application/x-www-form-urlencoded

Body grant_type=password&resource=https://graph.microsoft.com&client_id=<your client ID>&client_secret=<your client secret>&username=<username>&password=<password>

Output

If you refer the above steps, you will be able to generate access token and refresh token too.