If you are referring to just F-Secure Internet Security, you can then find that it supports Windows OS only as mentioned under Technical Details in the link here. I assume, your Acer smartphone should be coming with an Android OS.
If you are using F-Secure SAFE (as mentioned in one of your replies), I would recommend to contact our support so that they can look at your issue and troubleshoot further.
Is your code for...
F-Secure Safe or F-Secure Internet Security?
Unfortunately these are two different products! So make sure you got the right one.
Card reads F-SECURE SAFE Internet Security for all devices and is for 3 devices for 1year
Then call or chat with F-Secure customer support for further help!
May I know on which device/OS are you trying to enter the code for the IS? Have you tried to copy paste the code if you are typing it otherwise? Did it work?