@Chief1202 Here are a few follow-up questions to help diagnose the issue further:

Distance Check: How far is the Blink Sync module from the Deco unit, and have you tried moving it closer during the setup process?

Device Reboot: Have you rebooted both the Deco system and the Blink Sync module after switching to the 2.4 GHz only setting?

Network Configuration: Are there any specific security settings enabled on the Deco that could be preventing the Blink Sync module from connecting?

Reset Procedure: Have you tried resetting the Blink Sync module to factory settings before attempting to sync it again?

Network Visibility: When you set the Deco to 2.4 GHz only, did you check if the Blink Sync module could detect the Deco network during the setup process? 

Thanks, Dan