For GCM Encryption, the Initialization Vector will be converted and output as a Hexadecimal, even if you selected UTF-8.
This is demonstrated by the different IV values in the input/output bundles in the Encryption module, if hexadecimal is NOT selected:
Hence, in the Decryption module, you need to select Hexadecimal, IF you are reusing or directly mapping the Encryption module’s output IV variable.
This is clearly explained in Step 5: Decrypt the message (GCM ciphor algorithm) — AES (Advanced Encryption Standard) - Help Center, which says:
You could also leave the IV field empty in the Encryption module, and one will be generated for you (as a hexadecimal).
If in doubt, always check the documentation first.
For more information, see:
Hope this helps! If you are still having trouble, please provide more details.
— @samliew