Create a new PayIn and generate a payment link. Supports multiple payment methods:

• PSE (Pagos Seguros en Línea) for Colombia (COP)
  • Unique PayIns: Each PayIn is for a single transaction with a specific amount
  • Requires amount field
  • Requires bank_code field
• SPEI for Mexico (MXN)
  • Reusable PayIns: The same PayIn can be used multiple times for different amounts
  • Does NOT require amount field (user specifies amount when paying)
  • Does NOT require bank_code field

User information (document_type_id, document_number, full_names, email) is obtained from the user record via user_id.

Authentication: Both x-api-key header and Authorization: Bearer <token> header are required.