Cause
The X-Surveys-Contract header requests a version other than 1. details.supported lists the accepted ones.
What to do
Send X-Surveys-Contract: 1 or omit the header.
application/problem+json
{
"type": "https://masnet.com/developers/errors/unsupported_contract",
"title": "Unsupported contract",
"status": 406,
"detail": "...",
"code": "unsupported_contract",
"correlation_id": "..."
}