invalid_session API error

A signer or payer session is no longer valid.
The API returns HTTP 401; use requestId to trace the refusal.

{
  "error": "invalid_session",
  "message": "A signer or payer session is no longer valid.",
  "requestId": "req_a1b2c3d4e5f6"
}

What to do

A signer or payer session is no longer valid. Correct the request or state before retrying.