Replied 12 July 2018, 11:34 pm EST
The license agreement is one copy per developer and it is run-time royalty free. A developer can install it on up to three machines as long as that developer is the only one using it.
Hence, it seems that the serial key is already in use on three machines and you need to activate Spread on a fourth machine, then you have got to deactivate the Spread on one of the three machines. Else, you may get error while activating it on the fourth machine.
And if you cannot deactivate the serial key from old machines then you need to get your serial key reset by getting in touch with our sales team at below mentioned email address:-
For more information on licensing, you can visit our licensing FAQ here:
P.S. : Serial Key can be reset only once in lifetime.