This piece file does not contain the GSplit tags required by GUnite

I used gsplit to split a large backup file so it could be uploaded to my cloud account.
Now I need to restore some files in the backup due to an Raid Array crash. Unfortunatly; Gunite will not reconstitute the original file.

Asking for the first piece...
Reading first piece "R:\EaseUS_Backups\SmartBackups\Smart Backup\Smart Backup_20201216_Full_v1_001.gsd"
This piece file does not contain the GSplit tags required by GUnite. It cannot be united automatically.
Please select another piece file.

I tried just

copy /Z /B "Smart Backup_20201216_Full_v1_001.gsd"+"Smart Backup_20201216_Full_v1_002.gsd"+"Smart Backup_20201216_Full_v1_003.gsd"+"Smart Backup_20201216_Full_v1_004.gsd"+"Smart Backup_20201216_Full_v1_005.gsd" Smart_Backup_20201216_Full_v1_A.pdb

copy /Z /B "Smart Backup_20201216_Full_v1_006.gsd"+"Smart Backup_20201216_Full_v1_007.gsd"+"Smart Backup_20201216_Full_v1_008.gsd" Smart_Backup_20201216_Full_v1_B.pdb /B

copy /V /Z /B Smart_Backup_20201216_Full_v1_A.pdb+Smart_Backup_20201216_Full_v1_B.pdb "Smart Backup_20201216_Full_v1.pbd"

but the backup software does not recognize the file.

It looks like you mixed .pbd and pdb extensions in your copy lines. Can you double-check whether it’s the reason why the restore software does not recognize the restored file?

the final file has the correct extension.
So that isn’t the problem as far as I can tell.

I don’t see other problem in your copy lines. Since you united the file back, and there is no GSplit tags, you can try to contact the support team of your backup software and ask them why the file is not recognized.