Apple Watch Authentication Error on T-Mobile

Last Updated: Jan 12, 2022

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I purchased my new Apple Watch Series 3 with LTE on launch day, but couldn’t activate LTE on it because of an authentication error. After ten days of back and forth with T-Mobile support, I figured out a solution. In this article, I will tell you how to fix the activation error and enable LTE on your Apple Watch.

How you are supposed to activate LTE on your Apple Watch

Assuming everything else is in order, you can enable LTE on your Apple Watch during the initial pairing process. I skipped that step and instead, decided to do it later using the Watch app on my iPhone.

Inside the Watch app, I scrolled down to “Cellular.” From there, I followed the wizard, which loaded a T-Mobile web page that asked me to enter the last four digits of my social security number. I have a T-Mobile business account, so I had to enter the last four digits of my company’s Federal Employer Identification Number (FEIN). After entering it, I instantly got an “authentication” error and a screen suggesting to call customer care.

Apple’s new eSim could be the culprit

The Apple Watch Series 3 has a so-called embedded SIM (eSIM) that has its own International Mobile Equipment Identity (IMEI) number. Technically, it should be possible for a mobile carrier to enable LTE on your Apple Watch by adding the IMEI number to your phone plan. At least with T-Mobile that doesn’t seem to be the case. Instead, they require you to get a regular SIM card and add it to your account. Then they map your Apple Watch’s electronic ID (EID) to the new SIM card. Only then can you activate LTE on your Apple Watch.

T-Mobile customer care was unprepared

T-Mobile, like other mobile carriers, was utterly unprepared to deal with the activation issues. During the first few days after launch, T-Mobile didn’t even know what the problem was.

Apple Watch Series 3 - How to fix the authentication error on T-Mobile
I was running out of patience after ten days

After a few days, they had solved the issue on their end but suggested that Apple still had an issue. A few days later, Apple had apparently resolved the issue on their end too. But only for residential customers, as there was still a problem with business accounts. Long story, short, after ten days and a fruitless visit to the T-Mobile store, I could activate LTE on my new Apple Watch Series 3.

How to fix the authentication error and activate LTE

Note: T-Mobile told me that the following steps should work with other mobile carriers as well.

To activate LTE on your Apple Watch Series 3 on the T-Mobile network, you need to get a new line and thus a new SIM card. Once that new line is active (can take up to two hours), provide T-Mobile with the EID number of your Apple Watch. You can find the EID number in the Watch app on your iPhone, under General –> About –> EID. T-Mobile will then link the EID to your new SIM card.

  • Get a new line for your Apple Watch from T-Mobile (including a new SIM card)
  • Provide the EID number of your Apple Watch to T-Mobile
  • Have them link the EID to your new SIM card

In case you wonder, the new SIM card is also associated with a new phone number. But don’t worry, your Apple Watch won’t use that number, and instead, uses the number associated with your paired iPhone. T-Mobile leverages its DIGITS technology to link them together.

After referencing the EID with your new SIM card, it may take up to two hours for the changes to take effect. Despite T-Mobile’s suggestion, you don’t have to un-pair your Apple Watch. Just open the Watch app on your phone, click on Cellular and follow the activation process. I could activate LTE within minutes and I didn’t even have to wait for two hours.

What you don’t have to do

In case you talk to a rep who still doesn’t know the exact process, you don’t have to do any of the following steps:

  • Restart your iPhone or Apple Watch
  • Unpair the Apple Watch from your iPhone

But depending on your plan, you may have to go to a T-Mobile store to get your new SIM card. I had to do that.

Let me know if the above steps worked for you too!

2 thoughts on “Apple Watch Authentication Error on T-Mobile”

  1. Seems that no credit accounts still have the issue and they can’t correct it. It keeps asking for last 4 of social even though I never gave it to them. Day 5 now of working 3-4 hours each day.

  2. So how do you live with T-Mobile? Is there a way to get competent customer service? (Business account maybe?) We had terrible experience with their screw up on credit checks and on my iPad (pre-paid) I’ve had terrible problems with expired-SIM card, and they didn’t want to correct…


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