Not only FonePaw iOS Transfer, but also for other FonePaw products, you can try these solutions to sign in the full version. Here are some steps you may need:
1. Please check and confirm your email address and registration code whether you typed/pasted correctly.
2. Please check whether you download the correct version of program.
3. The installation and registration of program should be in the condition of Internet.
4. Any error message you got? If yes, send the screenshot to email@example.com to analyse and solve.