The prefix "camunda" for element "camunda:connector" is not bound"

I am constantly getting the error:

The prefix "camunda" for element "camunda:connector" is not bound.

Can someone tell me where the error is?

<?xml version="1.0" encoding="UTF-8"?>

<serviceTask id="sendMail" name="Send Mail Task">
  <extensionElements>
    <camunda:connector>
      <camunda:connectorId>mail-send</camunda:connectorId>
      <!-- input / output mapping -->
    </camunda:connector>
  </extensionElements>
</serviceTask>

Solution 1:

An XML namespace prefixed (camunda in this case) must be defined before use in order for XML to be namespace-well-formed.

Change

<serviceTask id="sendMail" name="Send Mail Task">

to

<serviceTask id="sendMail" name="Send Mail Task"
             xmlns:camunda="NAMESPACE-URI">

Check Camunda documentation for the proper value of NAMESPACE-URI. It will likely look like one of the following:

• http://camunda.org/schema/1.0/dmn
• http://camunda.org/schema/1.0/bpmn