diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index b50c2c4..cb90b66 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -8,6 +8,7 @@ kotest = "6.0.0.M10"
 kotlin = "2.1.20"
 kotlinBinaryCompatibilityPlugin = "0.18.1"
 kotlinLogging = "3.0.5"
+kotlixSerialization = "1.9.0"
 mockk = "1.14.5"
 quiver = "1.0.0"
 reflections = "0.10.2"
@@ -27,6 +28,7 @@ kotestJunitRunnerJvm = { module = "io.kotest:kotest-runner-junit5-jvm", version.
 kotestProperty = { module = "io.kotest:kotest-property", version.ref = "kotest" }
 kotlinLoggingJvm = { module = "io.github.microutils:kotlin-logging-jvm", version.ref = "kotlinLogging" }
 kotlinReflect = { module = "org.jetbrains.kotlin:kotlin-reflect", version.ref = "kotlin" }
+kotlinxSerializationCore = { module = "org.jetbrains.kotlinx:kotlinx-serialization-core", version.ref = "kotlixSerialization" }
 mockk = { module = "io.mockk:mockk", version.ref = "mockk" }
 quiver = { module = "app.cash.quiver:lib", version.ref = "quiver" }
 reflections = { module = "org.reflections:reflections", version.ref = "reflections" }
diff --git a/lib/build.gradle.kts b/lib/build.gradle.kts
index da13743..93c1ad1 100644
--- a/lib/build.gradle.kts
+++ b/lib/build.gradle.kts
@@ -25,6 +25,7 @@ dependencies {
   implementation(libs.arrow)
   implementation(libs.jooq)
   implementation(libs.kfsm)
+  implementation(libs.kotlinxSerializationCore)
   implementation(libs.quiver)
 
   // Test dependencies
diff --git a/lib/src/main/kotlin/xyz/block/domainapi/DomainApi.kt b/lib/src/main/kotlin/xyz/block/domainapi/DomainApi.kt
index 4e237ac..9d8c3fd 100644
--- a/lib/src/main/kotlin/xyz/block/domainapi/DomainApi.kt
+++ b/lib/src/main/kotlin/xyz/block/domainapi/DomainApi.kt
@@ -1,6 +1,7 @@
 package xyz.block.domainapi
 
 import java.time.LocalDate
+import kotlinx.serialization.Serializable
 
 /**
  * Interface of a service that executes a business process, for example, withdraw Bitcoin on-chain. It has the following
@@ -143,6 +144,7 @@ data class UpdateResponse<REQUIREMENT_ID, ATTRIBUTE_ID>(
 /**
  * Represent information sent from the server to the client.
  */
+@Serializable
 sealed class UserInteraction<REQUIREMENT_ID> {
   /**
    * An indication sent from the server to the client indicating that user action is required, e.g.,
@@ -150,6 +152,7 @@ sealed class UserInteraction<REQUIREMENT_ID> {
    *
    * @param id The id of the requirement. The parametrised type is typically an enumeration.
    */
+  @Serializable
   open class Hurdle<REQUIREMENT_ID>(val id: REQUIREMENT_ID) : UserInteraction<REQUIREMENT_ID>()
 
   /**
@@ -158,6 +161,7 @@ sealed class UserInteraction<REQUIREMENT_ID> {
    *
    *  @param id The id of the requirement. The parametrised type is typically an enumeration.
    */
+  @Serializable
   open class Notification<REQUIREMENT_ID>(val id: REQUIREMENT_ID) :
     UserInteraction<REQUIREMENT_ID>()
 }
@@ -165,6 +169,7 @@ sealed class UserInteraction<REQUIREMENT_ID> {
 /**
  * Represents an input into the system for a requirement.
  */
+@Serializable
 sealed class Input<REQUIREMENT_ID>(val id: REQUIREMENT_ID, val result: ResultCode) {
   /**
    * Represents the response to a server sent to the client.
@@ -172,6 +177,7 @@ sealed class Input<REQUIREMENT_ID>(val id: REQUIREMENT_ID, val result: ResultCod
    * @param id The id of the requirement. This is typically an enumeration.
    * @param code The result of attempting to overcome the hurdle.
    */
+  @Serializable
   open class HurdleResponse<REQUIREMENT_ID>(id: REQUIREMENT_ID, code: ResultCode) :
     Input<REQUIREMENT_ID>(id, code)
 
@@ -183,6 +189,7 @@ sealed class Input<REQUIREMENT_ID>(val id: REQUIREMENT_ID, val result: ResultCod
    *
    * @param id The id of the requirement whose result is needed to resume the process.
    */
+  @Serializable
   open class ResumeResult<REQUIREMENT_ID>(id: REQUIREMENT_ID) :
     Input<REQUIREMENT_ID>(id, ResultCode.CLEARED)
 }