Invoice questions

BASE_URL=${PEPAY_API_URL}

curl "$BASE_URL/api/v1/payments/invoice-questions" \
  -H "x-session-token: pst_..." \
  -H "x-signature: sig_..."

{
  "has_questions": true,
  "questions": {
    "questions": [
      {
        "id": "q1",
        "question": "Email address",
        "type": "email",
        "validation": { "required": true }
      }
    ]
  }
}