If you have lost your activation code you can always recover that from either
if you licensed SPAD.neXt before Nov. 2016:
SimMarket (https://secure.simmarket.com/). Just log into your SimMarket account and check the SPAD.neXt entry
if you licensed SPAD.neXt later than Nov. 2016
2Checkout (formerly avangate) https://secure.2co.com/myaccount/order_lookup/.
you can also log into your 2checkout/avangate account to recover the activation code in case you crated one.
if none of both works, send an email to support at spadnext.com from the email-address that your license is bound to.
(or open a ticket from within spad.next)
Also please note, if you license an additional addon, your activationkey will not change.