Context:

ANOM is a sting-operation ran by the FBI which involved a trojan horse smartphone and messaging app that was designed to be sold to criminal organisations to intercept their communications.

"""Legal restrictions""" prohibit the FBI from performing surveillance on their own citizens in this way, and therefore they would have been unable to monitor users of ANOM based in the United States if they performed the interception on home soil. By hosting the interception server in a country outside of their jurisdiction, the US would be able to make a loophole and perform surveillance without the legal provisions. The ANOM operation involved three countries, the third being a European Union member.

404 Media (Jason Koebler, Emanuel Maiberg, Samantha Cole, and Joseph Cox) claim the third country is Lithuania. The remainder of the article is paywalled but what is viewable for free is enough for a good description.