iOS 15.4 - iMessage won't active. Error message - "An error occurred during activation."

I think it has alot to do with the esims. I had the same problem, i removed my cellular plan from my phone and as i tried to add it back it would not allow me to do so. I went to tmobile and they gave me a physical sim which then added my number back on my phone and then activated with iMessage.

This very thing happened to me after updating to 15.4. Went back and forth between T-Mobile and Apple, each blaming the other, reset network, reset phone TWICE until that whole iCloud outage was resolved and it coincidentally started working again a few days after it broke. Now it's just started happening again to me. My phone has been on 15.4.1 since it rolled out but it only started this nonsense again today. I too have a T-Mobile e-sim only. May go by the store to pick up a physical sim tomorrow if it hasn't sorted itself out. This is definitely a widespread bug that neither party has really acknowledged and sought to resolve.

Yesterday I inserted physical sim without number to my phone it turned off cellular, then I removed it and iMessage started to work. It’s been more then 28 hours since then, so hopefully it helped. Before that iMessage worked about 2 hours a day. Fingers crossed.

I was having the same issues since update to iOS 15.4 and I am also on T-Mobile with eSIM. What I did notice is when my bubbles turn green, i go to iMessage within settings and the spinning wheel was stuck next to my phone number. Exiting messages app and opening it again was fixing everything. Since around 4/10 I haven’t seen those issues again, maybe it was really something with T-Mobile eSIM and they just fixed it?

As other’s have mentioned, I went to T-Mobile, for a physical sim and the problem immediately went away. The T-Mobile rep even mentioned that Apple’s implementation of e-sim has caused a lot of problems. It might just be on T-Mobile but just get a physical sim.

I am having the exact same issue. I've been on the phone with Apple and T-Mobile for over 4 hours in total. I was bounced back and forth between Apple and T-Mobile, but now Apple has take on full responsibility and escalated to engineering. They said they had a fix and to wait 24-48 hours. I waited longer and it appeared to be fixed, then 48 hours later the dreaded "Activation unsuccessful" reappeared. Apple Support wants to setup another call.

Like others on here, I am on T-Mobile eSIM. I am going to pass this thread along to Apple Support.

I'd prefer to not have a physical SIM as I travel internationally and there are times I need a pre-paid SIM for data. So has anyone re-provisioned with eSIM have this fixed permanently?

After hours of trying EVERYTHING removing the Sim and readding it to the phone worked perfectly and iMessage and FaceTime added themselves within seconds.

Remove Cellular Account, Restart the phone, connect to wifi, go to add cellular account and scan the QR code mobile sent you and instantly works.

They really need to address this because less tech savvy people will never figure this out and it was driving me mad.

I have solved this issue with my 13 pro max and t-mobile. My iPhone had an e-sim originally. The tmobile store said they have seen this before and that for some reason the e-sim gets disconnected. They installed a physical sim, reset the network settings, and now iMessage will activate with my phone number as it should.

Good luck everyone!

iOS updates, particularly in USA, sometimes need a carrier update.

If you cannot find the update in Settings, General, About then with the phone on you can either take out the SIM and put it back a couple of times or remove the eSIM plan.

This was pointed out by many posters and the act of removing the plan stimulates the carrier update to be installed.

I’m T-Mobile as well and I skipped a carrier update and can’t get it to reappear. Guess I need to uninstall and reinstall the cell plan but dubious about doing it.

Apple said via a phone call that they are aware and are working on a patch.

For me it’s a daily thing. I wake up, iMessage has started working again, couple hours later my number is not part of my appleid, I add it, and the “24 hrs” starts over again with it working when I wake up the next day.

It was helpful but did not solve your problem, there is a difference. We here are users like you trying to help. Take the advice or ignore it I really don't care but I hate ingratitude.

All my phones work on ios15.4.1 so I cannot possibly see how this can be a problem with anything other than your carrier.

I'm off, don't bother to respond.

Thank you again for posting this information. I did the same to have my eSIM "reset" and Activation of iMessage worked almost immediately.

I won't claim victory for the next 48 hours but things are looking good.

I will say that T-Mobile was a pain. I got bounced to three different agents as they needed a "Tech Expert" to do this.

I recommend not turning off iMessage. I did that to tey to resolve a specific bug with iMessage, and now I can’t turn iMessage back on. I also went through Apple Support to troubleshoot the other issue (unresolved, awaiting a call from support), including restarting my phone, and now I have two separate issues. Seems like iOS 15.4.1 introduced multiple iMessage bugs.

I'm on a T-Mobile ESim as well. I've been having the same issue for weeks. I removed my cellular plan and had T-Mobile service added back on. I did this by calling T-Mobile and giving them my EID.

Now, I can quickly activate iMessage with no problems, and everything seems normal. I'll update in a few days to confirm that this resolved the issue.

I can now confirm that after 5 days the solution posted by JustJared works. For some it will be faster to get a hardware SIM at a local T-Mobile store, but I wanted to keep the slot open as I sometimes need to purchase a cheap Data only SIM while traveling internationally. More and more international locations support eSIM, but not all.

To summarize the solution that worked for me is to delete my existing eSIM cellular plan. Call T-Mobile and provide your EID (found in General -> About) so they can activate the plan on your phone.

This is a pretty specific problem that appears to affect T-Mobile subscribers and a bug in 15.4 and 15.4.1 where delaying installation of an updated Carrier Profile prevents you from installing it later by going to General->About as instructed.

So Apple's "Recommended solution" applies to most others, but not this specific instance. So I wish the higher level members of the Support Community would read the entire discussion before reposting the same information found at Apple Support.