you show an example of a contact with actions:
<action id="send_to_vm" dial="104" dial_prefix="" label="Voicemail" name="Dial Voicemail">
<headers>
<header key="X-Digium-Call-Feature" value="feature_send_to_vm" />
<header key="Diversion" value="<sip:%_ACCOUNT_USERNAME_%@%_ACCOUNT_SERVER_%:%_ACCOUNT_PORT_%>;reason="send_to_vm"" />
</headers>
</action>
There is a small typo here: at the end of the line with the Diversion key you are missing a ">" tag in order to close the xml bracket.
Ronny