diff --git a/webapi/src/test/scala/org/knora/webapi/slice/admin/domain/model/UserSpec.scala b/webapi/src/test/scala/org/knora/webapi/slice/admin/domain/model/UserSpec.scala
index 8a840087fa..9d38569890 100644
--- a/webapi/src/test/scala/org/knora/webapi/slice/admin/domain/model/UserSpec.scala
+++ b/webapi/src/test/scala/org/knora/webapi/slice/admin/domain/model/UserSpec.scala
@@ -7,8 +7,6 @@ package org.knora.webapi.slice.admin.domain.model
 
 import zio.test.*
 
-import dsp.valueobjects.IriErrorMessages
-
 object UserSpec extends ZIOSpecDefault {
   private val validUserIri            = "http://rdfh.ch/users/jDEEitJESRi3pDaDjjQ1WQ"
   private val userIriWithUUIDVersion3 = "http://rdfh.ch/users/cCmdcpn2MO211YYOplR1hQ"
@@ -22,46 +20,42 @@ object UserSpec extends ZIOSpecDefault {
 
   private val usernameSuite = suite("Username")(
     test("Username must not be empty") {
-      assertTrue(Username.from("") == Left(UserErrorMessages.UsernameMissing))
+      assertTrue(Username.from("") == Left("Username cannot be empty."))
     },
     test("Username may contain alphanumeric characters, underscore and dot") {
       assertTrue(Username.from("a_2.3").isRight)
     },
     test("Username has to be at least 4 characters long") {
-      assertTrue(Username.from("abc") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("abc") == Left("Username is invalid."))
     },
     test("Username has to be at most 50 characters long") {
       assertTrue(
-        Username
-          .from("123456789012345678901234567890123456789012345678901")
-          .left
-          .exists(_.equals(UserErrorMessages.UsernameInvalid))
+        Username.from("123456789012345678901234567890123456789012345678901") == Left("Username is invalid.")
       )
     },
     test("Username must not contain other characters") {
-      assertTrue(
-        Username.from("a_2.3!") == Left(UserErrorMessages.UsernameInvalid),
-        Username.from("a_2-3") == Left(UserErrorMessages.UsernameInvalid),
-        Username.from("a.b@example.com") == Left(UserErrorMessages.UsernameInvalid)
-      )
+      val invalid = List("a_2.3!", "a_2-3", "a.b@example.com")
+      check(Gen.fromIterable(invalid)) { i =>
+        assertTrue(Username.from(i) == Left("Username is invalid."))
+      }
     },
     test("Username must not start with a dot") {
-      assertTrue(Username.from(".abc") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from(".abc") == Left("Username is invalid."))
     },
     test("Username must not end with a dot") {
-      assertTrue(Username.from("abc.") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("abc.") == Left("Username is invalid."))
     },
     test("Username must not contain two dots in a row") {
-      assertTrue(Username.from("a..bc") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("a..bc") == Left("Username is invalid."))
     },
     test("Username must not start with an underscore") {
-      assertTrue(Username.from("_abc") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("_abc") == Left("Username is invalid."))
     },
     test("Username must not end with an underscore") {
-      assertTrue(Username.from("abc_") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("abc_") == Left("Username is invalid."))
     },
     test("Username must not contain two underscores in a row") {
-      assertTrue(Username.from("a__bc") == Left(UserErrorMessages.UsernameInvalid))
+      assertTrue(Username.from("a__bc") == Left("Username is invalid."))
     }
   )
 
@@ -70,22 +64,26 @@ object UserSpec extends ZIOSpecDefault {
       assertTrue(Email.from("j.doe@example.com").isRight)
     },
     test("Email must not be empty") {
-      assertTrue(Email.from("") == Left(UserErrorMessages.EmailMissing))
+      assertTrue(Email.from("") == Left("Email cannot be empty."))
     },
     test("Email must not be a username") {
-      assertTrue(Email.from("j.doe") == Left(UserErrorMessages.EmailInvalid))
+      assertTrue(Email.from("j.doe") == Left("Email is invalid."))
     }
   )
 
   private val iriSuite = suite("UserIri")(
     test("pass an empty value and return an error") {
-      assertTrue(UserIri.from("") == Left(UserErrorMessages.UserIriMissing))
+      assertTrue(UserIri.from("") == Left("User IRI cannot be empty."))
     },
     test("pass an invalid value and return an error") {
-      assertTrue(UserIri.from(invalidIri) == Left(UserErrorMessages.UserIriInvalid(invalidIri)))
+      assertTrue(UserIri.from(invalidIri) == Left(s"User IRI: $invalidIri is invalid."))
     },
     test("pass an invalid IRI containing unsupported UUID version and return an error") {
-      assertTrue(UserIri.from(userIriWithUUIDVersion3) == Left(IriErrorMessages.UuidVersionInvalid))
+      assertTrue(
+        UserIri.from(userIriWithUUIDVersion3) == Left(
+          "Invalid UUID used to create IRI. Only versions 4 and 5 are supported."
+        )
+      )
     },
     test("pass a valid value and successfully create value object") {
       assertTrue(UserIri.from(validUserIri).isRight)
@@ -94,7 +92,7 @@ object UserSpec extends ZIOSpecDefault {
 
   private val givenNameSuite = suite("GivenName")(
     test("pass an empty value and return an error") {
-      assertTrue(GivenName.from("") == Left(UserErrorMessages.GivenNameMissing))
+      assertTrue(GivenName.from("") == Left("GivenName cannot be empty."))
     },
     test("pass a valid value and successfully create value object") {
       assertTrue(GivenName.from(validGivenName).isRight)
@@ -103,7 +101,7 @@ object UserSpec extends ZIOSpecDefault {
 
   private val familyNameSuite = suite("FamilyName")(
     test("pass an empty value and return an error") {
-      assertTrue(FamilyName.from("") == Left(UserErrorMessages.FamilyNameMissing))
+      assertTrue(FamilyName.from("") == Left("FamilyName cannot be empty."))
     },
     test("pass a valid value and successfully create value object") {
       assertTrue(FamilyName.from(validFamilyName).isRight)
@@ -112,7 +110,7 @@ object UserSpec extends ZIOSpecDefault {
 
   private val passwordSuite = suite("Password")(
     test("pass an empty value and return an error") {
-      assertTrue(Password.from("") == Left(UserErrorMessages.PasswordMissing))
+      assertTrue(Password.from("") == Left("Password cannot be empty."))
     },
     test("pass a valid value and successfully create value object") {
       assertTrue(Password.from(validPassword).isRight)
@@ -121,7 +119,7 @@ object UserSpec extends ZIOSpecDefault {
 
   private val passwordHashSuite = suite("PasswordHash")(
     test("pass an empty value and return an error") {
-      assertTrue(PasswordHash.from("", pwStrength) == Left(UserErrorMessages.PasswordMissing))
+      assertTrue(PasswordHash.from("", pwStrength) == Left("Password cannot be empty."))
     },
     test("pass a valid value and successfully create value object") {
       val passwordString = "password1"
@@ -141,7 +139,7 @@ object UserSpec extends ZIOSpecDefault {
       )
     },
     test("pass an invalid password strength value and return an error") {
-      assertTrue(PasswordStrength.from(-1) == Left(UserErrorMessages.PasswordStrengthInvalid))
+      assertTrue(PasswordStrength.from(-1) == Left("PasswordStrength is invalid."))
     },
     test("pass a valid password strength value and create value object") {
       assertTrue(PasswordStrength.from(12).isRight)