You should first check if your account could send/receive trade offer (whether Steam guard has been enabled for over 15 days).
P.S. I google translated your question, so someone correct me if I am wrong.
I'll translate to spanish if you don't mind Joto:
Primero debes mirar si tu cuenta de Steam puede enviar/recibir ofertas de intercambio (es decir, si Steam guard ha estado al menos 15 días activo).