If the Retransmit Request is for a previous UUID, that value should be used. Otherwise, the then put that here otherwise put default null value should be used.
0 – Default CME assigned UUID or Last UUID used in last Establish message.for any messages to be sent to customer before first customer Establish of the week.
UUID from any previous Establish in the current week (Sunday-Friday)
Max value is 9223372036854775807