T-Mobile said Tuesday that it had not blocked iCloud Private relay, and that it had identified what was causing some iPhone users to appear blocked from using the feature.

“Overnight our team identified that in the 15.2 iOS release, some device settings default to the feature being toggled off. We have shared this with Apple. This is not specific to T-Mobile. Again though, we have not broadly blocked iCloud Private,” the company told Bloomberg reporter Mark Gurman.

iCloud Private Relay lets users hide the websites they visit from third parties, according to a report from 9to5Mac. The VPN-like Private Relay hides your web activity from any outside sources — including Apple and your carrier — and prevents anyone from identifying you or the sites you access. It’s currently available via a subscription to iCloud Plus.

Private Relay is still in beta in iOS 15 and iPadOS 15, and it isn’t turned on by default. You have to go into your iPhone’s settings to switch it on, which is where some T-Mobile customers first noticed the message above appearing.

In a reply to that tweet, the user shows what happens when you click the “Learn More” button below the initial message — there, Apple explains why T-Mobile might be blocking the feature. “Networks that require the ability to audit traffic or perform network-based filtering will block access to Private Relay,” it reads. “Your cellular provider may be providing network-based services, such as Parental Controls, requiring them to view the traffic on your network.”

According to The T-Mo Report, iCloud Private Relay conflicts with a number of T-Mobile services, but that doesn’t appear to be the case here.

According to 9to5Mac, iPhone users in Europe were the first to notice that access to the Private Relay feature wasn’t working. T-Mobile, Vodafone, and Telefonica added their names to an open letter published in The Telegraph that criticizes the feature. Carriers argue that Private Relay “will impair others to innovate and compete in downstream digital markets and may negatively impact operators’ ability to efficiently manage telecommunication networks.”

Update January 11th, 4:48AM ET: Updated with additional reporting by The T-Mo Report.

Update January 11th 3:00PM ET: Updated throughout with comment from T-Mobile about the cause of the issue.