Normally, voluntary redundancy would be done as an agreed set of terms conditions, as you're being asked to give up employment terms and conditions. Typically you would expect some form of payment.
However, if you don't have such an agreement, all that's happened is the employer has asked for people to resign and some have obliged, in which case there's no payment due as none was agreed. People don't get paid for resigning.
So it all depends on what was agreed beforehand.