If you have a Lightning address in your Nostr profile, this concerns you directly.

There is a good chance that address resolves through Spark, a Bitcoin Layer 2 run by two companies, Lightspark and Flashnet. Wallet of Satoshi runs on it. Cake Wallet runs on it. The Breez SDK defaults to it. Every transfer on Spark is co-signed, and therefore seen, by the operators. Users were never told, and that is presented as a feature.

Your funds are safe. The custody design is genuinely good. But custody and privacy are different things, and here is the part that matters on Nostr: your npub is public, your Lightning address is in your profile, and the operator sees every payment behind that address. Link the two and a pseudonym becomes a named person with a queryable payment history. SparkStalker already demonstrated this works. And unlike Lightning proper, where the data to subpoena never existed, Spark's operators are named, regulated companies that can be compelled to hand over what they see.

It does not stop at Spark users. Lightning privacy is a crowd effect. Every wallet that moves behind Spark's operator thins the crowd for everyone else, including people running their own nodes. Zap someone on Wallet of Satoshi and the operator records it, whether you ever agreed to Spark or not.

I wrote three articles on this. What Spark is and who runs it. Why a public identity turns its metadata into a warrant target. And why "then don't use it" misses the argument.

Your Lightning wallet might not be a lightning wallet
https://btc2bgroup.com/news/you-are-already-using-spark

Your Nostr profile is a subpoena waiting to happen
https://btc2bgroup.com/news/spark-nostr-and-the-warrant-problem

The privacy you lose when others choose Spark
https://btc2bgroup.com/news/the-privacy-you-lose-when-others-use-spark