Can't validate a SparkPost delivery server


I have SparkPost delivery servers configured on my live server. I need to create one on my local environment for testing, I'm using the same SparkPost API key, but the server does not validate.
What could be the issue?

I need this to debug the template parsing, because Mailwizz is inserting the tracking transparent image inside the template body, it's most likely caused by an extension, but to debug it I need a delivery server configured so the campaign sending takes place.

I get this error:

  • Cannot send the confirmation email using the data you provided.
  • POST to webhook target URL failed with non-2xx response code 502
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