AT&T NumberSync stopped working on my Galaxy Watch 4

Hi, Atlutd17! We understand communication is key! We really appreciate your patience while we work towards repairing NumberSync!

We'd like to invite you into a direct message which is the chat icon next to the bell icon in the upper right corner of the Forums so we can check on the status of your case. In the meantime try using the steps provided in @earldav comment which is below yours. It helped resolve their error.

We look forward to working with you!

Jonye, AT&T Community Specialist 

I was having the same problem. It was caused by using a VPN on my phone. Try turning off your VPN and attempting to reconnect numbersync

Obviously I'm still paying for and LTE line for my Galaxy watch which doesn't work with numbersync anymore and I tried to deal with billing and they say I have to keep paying until there's a resolution. That's a bunch of crap. My question is how long ago did AT&T know about this and not notified the customers that there was an issue? How much money do they owe us now? They told me just last week that I wouldn't have to still keep paying for my LTE line regardless of whether it worked or not until they found a resolution oh, how long is that going to be a year? My question is to a T and T how long ago did you know about this issue? And why didn't AT&T notify customers of this issue? I've been with AT&T for 18 years and I'm really (Edited per community guidelines) now. I need my watch to have its own line as I can't carry my phone with me at all times.

Found a solution. The mobile plan needs to be deleted and a new plan installed. Numbersync working again! I think you have to talk to a service rep to get that done. 

I keep getting a PD-SDK-server_error

This is on a galaxy watch 4 classic and S22 Ultra, I've already received the esim for the watch.

I was getting them too.  Go to Att corporate store, request a new esim.  Call att with rep and have your existing watch line deleted/removed.   Reset watch, add new line with qr code, do numbersync, then you should be all set. 

I'm having same problem with my husband's samsung watch 4 classic. My watch is synced to my phone but his will not sync to his. I have set him up a user ID but get a message that his number already has a user ID His phone is listed on my account so it is listed with my  user ID since we are on same phone plan. How can I get his number to be assigned to his user ID without taking it off my phone plan?

Well I finally got it working, but I didn't have to go to the ATT store,  there were some FAQ's that I followed.  On my phone I needed to uninstall, Galaxy Wear then reinstall, and then go through the whole process from scratch like this was a new phone for this watch.  Since the watch already had the Mobile data plan from the first time, it went through the Number sync process again and actually sync'd this time.

Bad part is I had to do all the previous customizations all over again, faces, apps, quick keys, etc

Just remember the whole time your number sink hasn't been working which could go way back as you may not have known it crashed you have been charged by at&t. That's my main battle with them right now, first and foremost I still don't have a number sync working with my Galaxy watch for classic and secondly I was told when and if number six starts working then I can go back and request a refund so they are charging you for services you are not getting which is really really screwed up. I got into it with tech support this past week and after 18 years of being with AT&T I'm seriously considering going elsewhere. They said they're going to have a loyalty call me and of course I never heard a (Edited per community guidelines) thing. I'll give it one more shot and then I'm going to expect that I get reimbursed from the day they first noticed number sync going south which was according to tech support last year. I'm furious.

EARLDAV: I tried your suggestion and that didn't work either.