If you intend to process recurring payments it is important to indicate this in your transactions.

For testing, set the following fields after selecting the "Try It" button
externalReferenceID = Unique record identifier for processing - you assign Numeric Min = 16 Max 19
transactionDate = Set to UTC timezone, Format 2020-09-15T17:01:01
Link to UTC time = https://time.is/UTC

Click Try It! to start a request and see the response here!