[APP] Campaigner

**Name of app / service**
Campaigner
https://www.campaigner.com/

**Link to developer documentation**
https://media.campaigner.com/media/30/304640/CampaignerRESTAPIUserManual.pdf

Context:
The test request failed. I tried the simpler sample from documentation. I also instructed Claude to give me the minimal complying XML based on Campaigner's Search Criteria [XSD](https://ws.campaigner.com/2013/01/ContactsSearchCriteria2.xsd), and this also failed. An XML filtering against Contacts with status "Subscribed" also failed, I did this attempt because I confirm the Campaigner account already has at least one contact with "Subscribed" status.
Consistently, test request fails with:

> {
> "response_code": 106,
> "response_message": "Invalid Search XML",
> "response_details": ""
> }