NumberSync Error Code sd-sdk-400

I had the same problem. I tried working with AT&T Tech Support for 4 days after the retail store rep could not figure it out. No one knows how to resolve. Finally, I was so frustrated I nearly canceled all services w/AT&T. They advised me to return the watch before the 14-day cutoff. I am waiting for my new watch to arrive and I plan to  have the tech at the store open the box and get it working before I leave the store!

Thank you!!!! definitely I will try that because I also have spent so many hours with the  AT&T Tech Support and also went to a store with no luck.

Thank you :-)

Hi williv1, we are here to help with your error code SD-SDK-400 when syncing your Samasung Galaxy Watch 5 to your Galaxy Z Fold 3 device!

This error code is now resolved, and you should be able to set up your numbersync again by:

1. Getting the Samsung Galaxy Wearable app and making sure you have the most recant version of the app.
2. Making sure that Bluetooth is turned on for both your wearable and your smartphone.
3. You have paired your smartphone and wearable using the Samsung pairing process.
4. You have an active wireless plan for your wearable
5. You have a NumberSync user ID for your wearable.

Then follow the set up process mentioned by previous agent. If this doesnt help, check out our troubleshoot & resolve tool to help fix your numbersync concerns. You'll need to sign in or navigate to Fix my wireless>Connection>Messaging to get started.

Feel free to reach back to us if you need additional help, we'll pull you in to private and troubleshoot on our end!

Thank you for posting on the AT&T Community Forums!

Rhoda, AT&T Community Specialist

Hi Rhoda, is there a fix for my case?

We definitely want to look further into the error message your receiving when connecting to AT&T Numbersync from your wearable, @emelindao.

Based on the detailed information you've provided, we want to bring you into a Direct Message for further support. Please check the message icon in the upper portion of the forums page and reply back to us. 

In the meantime, we do suggest that you continue to try the steps listed above by Rhoda to see if the error code still persist. 

We can't wait to hear back from you, and thanks for reaching out to the AT&T Community Forums.

Lynn, AT&T Community Specialist

I am also experiencing the issue emelindao is having. I tried the troubleshooting steps above and it still doesn't work. My watch keeps giving an error when trying to add an ID to its number.

Hey there @Colton_Allison, we want to help you set up NumberSync.

Based on the information you provided, we'd like to continue this conversation in a DM to better assist you. Please check the message icon in the upper right-hand corner of this page for our message. 

In the meantime, please have your account information at the ready.

We look forward to hearing from you.

Dylan, AT&T Community Specialist

The solution posted by Rhoda  (Fix my wireless>Connection>Messaging) did not work to solve my issue. Apparently, Code SD-SDK-400 is an known issue. I had to open a ticket while in the retail store today. I ordered a new watch and the same error code was invoked. When I called techsupport, I was routed to the "advanced tech support" team. Waiting to see if I get a call back. I will escalate if necessary. There were so many customer service missteps, I lost count.

Ohhh WOW really, so disappointed 😞 

This is an update. I just tried another option using "Fix my wireless" where I was able to select both my phone and the watch to check compatibility for the NumberSync feature. This is what came back "We're sorry. The selected devices won't work with each other using NumberSync. But, you have some options..."