Rest API working in Desktop but when published online it is returning Error 405

Hey,

I set up a API datasource in Power BI desktop. The whole model is working fine. Once I publish the report, there seems to be an error 405 when accessing the API datasources. No idea how to fix this. 

Failed to update data source credentials: Web.Contents failed to get contents from 'https://[not disclosed]' (405): Method Not AllowedHide details

The data source is basically a function to call an API several times (because I can only call for a period of max 30days.

This is the function:

let function = (startdate as text, enddate as text) => let
Login = Json.Document(Web.Contents("https://[not disclosed]", [Headers=[#"Content-Type"="application/x-www-form-urlencoded", Accept="application/json"], Content=Text.ToBinary("username=-----&password=------&market=BE")])),
sessionId = Login[sessionId],
body = "{
""from"": """& startdate &""",
""to"": """& enddate &""",
""events"": [],
""venues"": [],
""admin"": [],
""promoter"": []
}",
Source=Json.Document(Web.Contents("https://[not disclosed]", [Headers=[#"sessionId"=sessionId, #"marketcode"="BE", Accept="application/json",#"Content-Type"="application/json"], Content=Text.ToBinary(body)])),
transactions = Source[transactions],
#"Converted to Table" = Table.FromList(transactions, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
#"Expanded Column1" = Table.ExpandRecordColumn(#"Converted to Table", "Column1", {"firstName", "lastName", "middleName", "email1", "email2", "phone1", "phone2", "phone3", "phone4", "address1", "address2", "zipCode", "city", "country", "customerNumber", "preferredLang", "company", "department", "gdprFlags", "eventId", "eventCode", "eventDate", "eventTime", "eventTitle", "venueId", "venue", "promoter", "administrator", "keywords", "level", "section", "row", "seatNumber", "price", "priceCategory", "priceType", "trxHeaderCode", "transactionDate", "transactionTime", "orderNumber", "orderNote", "status", "outletCode", "outletName", "cameFromCode"}, {"Column1.firstName", "Column1.lastName", "Column1.middleName", "Column1.email1", "Column1.email2", "Column1.phone1", "Column1.phone2", "Column1.phone3", "Column1.phone4", "Column1.address1", "Column1.address2", "Column1.zipCode", "Column1.city", "Column1.country", "Column1.customerNumber", "Column1.preferredLang", "Column1.company", "Column1.department", "Column1.gdprFlags", "Column1.eventId", "Column1.eventCode", "Column1.eventDate", "Column1.eventTime", "Column1.eventTitle", "Column1.venueId", "Column1.venue", "Column1.promoter", "Column1.administrator", "Column1.keywords", "Column1.level", "Column1.section", "Column1.row", "Column1.seatNumber", "Column1.price", "Column1.priceCategory", "Column1.priceType", "Column1.trxHeaderCode", "Column1.transactionDate", "Column1.transactionTime", "Column1.orderNumber", "Column1.orderNote", "Column1.status", "Column1.outletCode", "Column1.outletName", "Column1.cameFromCode"}),
#"Renamed Columns" = Table.RenameColumns(#"Expanded Column1",{{"Column1.firstName", "firstName"}, {"Column1.lastName", "lastName"}, {"Column1.middleName", "middleName"}, {"Column1.email1", "email1"}, {"Column1.email2", "email2"}, {"Column1.phone1", "phone1"}, {"Column1.phone2", "phone2"}, {"Column1.phone3", "phone3"}, {"Column1.phone4", "phone4"}, {"Column1.address1", "address1"}, {"Column1.address2", "address2"}, {"Column1.zipCode", "zipCode"}, {"Column1.city", "city"}, {"Column1.country", "country"}, {"Column1.customerNumber", "customerNumber"}, {"Column1.preferredLang", "preferredLang"}, {"Column1.company", "company"}, {"Column1.department", "department"}, {"Column1.gdprFlags", "gdprFlags"}, {"Column1.eventId", "eventId"}, {"Column1.eventCode", "eventCode"}, {"Column1.eventDate", "eventDate"}, {"Column1.eventTime", "eventTime"}, {"Column1.eventTitle", "eventTitle"}, {"Column1.venueId", "venueId"}, {"Column1.venue", "venue"}, {"Column1.administrator", "administrator"}, {"Column1.keywords", "keywords"}, {"Column1.promoter", "promoter"}, {"Column1.level", "level"}, {"Column1.section", "section"}, {"Column1.row", "row"}, {"Column1.seatNumber", "seatNumber"}, {"Column1.price", "price"}, {"Column1.priceCategory", "priceCategory"}, {"Column1.trxHeaderCode", "trxHeaderCode"}, {"Column1.transactionDate", "transactionDate"}, {"Column1.transactionTime", "transactionTime"}, {"Column1.orderNumber", "orderNumber"}, {"Column1.orderNote", "orderNote"}, {"Column1.status", "status"}, {"Column1.outletCode", "outletCode"}, {"Column1.outletName", "outletName"}, {"Column1.cameFromCode", "cameFromCode"}})
in
#"Renamed Columns"
in
function