Afghanistan is not a party to the Hague Service Convention and has no service treaty with the United States. The Taliban have controlled the country since August 2021, the United States does not recognize them as Afghanistan's government, and the U.S. Embassy in Kabul suspended operations in August 2021. Official channels, including Letters Rogatory, are not a dependable route.
The Taliban and many of its members are subject to U.S. sanctions, so any arrangement that could involve Taliban-controlled authorities needs legal review first. Depending on the defendant's location, service through a local agent, or a method your court orders under FRCP Rule 4(f)(3), may be possible. Many Afghans have left the country since 2021, so confirming the defendant's current location often comes first.