diff --git a/app/controllers/repp/v1/domains_controller.rb b/app/controllers/repp/v1/domains_controller.rb
index 05cb5b754..dcf7a15cb 100644
--- a/app/controllers/repp/v1/domains_controller.rb
+++ b/app/controllers/repp/v1/domains_controller.rb
@@ -27,7 +27,7 @@ module Repp
       desc 'Create a new domain'
       param :domain, Hash, required: true, desc: 'Parameters for new domain' do
         param :name, String, required: true, desc: 'Domain name to be registered'
-        param :registrant_id, String, required: true, desc: 'Registrant contact code'
+        param :registrant, String, required: true, desc: 'Registrant contact code'
         param :period, Integer, required: true, desc: 'Registration period in months or years'
         param :period_unit, String, required: true, desc: 'Period type (month m) or (year y)'
         param :nameservers_attributes, Array, required: false, desc: 'Domain nameservers' do
@@ -170,7 +170,7 @@ module Repp
       def forward_registrar_id
         return unless params[:domain]
 
-        params[:domain][:registrar_id] = current_user.registrar.id
+        params[:domain][:registrar] = current_user.registrar.id
       end
 
       def set_domain
@@ -216,7 +216,7 @@ module Repp
       end
 
       def domain_create_params
-        params.require(:domain).permit(:name, :registrant_id, :period, :period_unit, :registrar_id,
+        params.require(:domain).permit(:name, :registrant, :period, :period_unit, :registrar,
                                        dnskeys_attributes: [%i[flags alg protocol public_key]],
                                        nameservers_attributes: [[:hostname, ipv4: [], ipv6: []]],
                                        admin_contacts: [],
diff --git a/app/interactions/actions/domain_create.rb b/app/interactions/actions/domain_create.rb
index 4534dfa5e..ec6e83b0e 100644
--- a/app/interactions/actions/domain_create.rb
+++ b/app/interactions/actions/domain_create.rb
@@ -66,16 +66,16 @@ module Actions
     end
 
     def assign_registrant
-      unless params[:registrant_id]
+      unless params[:registrant]
         domain.add_epp_error('2306', nil, nil, %i[registrant cannot_be_missing])
         return
       end
 
-      regt = Registrant.find_by(code: params[:registrant_id])
+      regt = Registrant.find_by(code: params[:registrant])
       if regt
         domain.registrant = regt
       else
-        domain.add_epp_error('2303', 'registrant', params[:registrant_id], %i[registrant not_found])
+        domain.add_epp_error('2303', 'registrant', params[:registrant], %i[registrant not_found])
       end
     end
 
@@ -207,7 +207,7 @@ module Actions
     end
 
     def current_registrar
-      Registrar.find(params[:registrar_id])
+      Registrar.find(params[:registrar])
     end
   end
 end
diff --git a/app/interactions/actions/domain_update.rb b/app/interactions/actions/domain_update.rb
index e93162fd5..0df036654 100644
--- a/app/interactions/actions/domain_update.rb
+++ b/app/interactions/actions/domain_update.rb
@@ -49,7 +49,7 @@ module Actions
 
       regt = Registrant.find_by(code: params[:registrant][:code])
       unless regt
-        domain.add_epp_error('2303', 'registrant', params[:registrant_id], %i[registrant not_found])
+        domain.add_epp_error('2303', 'registrant', params[:registrant], %i[registrant not_found])
         return
       end
 
@@ -234,7 +234,7 @@ module Actions
     def ask_registrant_verification
       if verify_registrant_change? && !bypass_verify &&
          Setting.request_confirmation_on_registrant_change_enabled
-        domain.registrant_verification_asked!(params, params[:registrar_id])
+        domain.registrant_verification_asked!(params, params[:registrar])
       end
     end
 
diff --git a/lib/deserializers/xml/domain.rb b/lib/deserializers/xml/domain.rb
index c663d4e7e..e406a8de7 100644
--- a/lib/deserializers/xml/domain.rb
+++ b/lib/deserializers/xml/domain.rb
@@ -11,8 +11,8 @@ module Deserializers
       def call
         attributes = {
           name: if_present('name'),
-          registrar_id: registrar,
-          registrant_id: if_present('registrant'),
+          registrar: registrar,
+          registrant: if_present('registrant'),
           reserved_pw: if_present('reserved > pw'),
         }
 
diff --git a/test/integration/repp/v1/domains/create_test.rb b/test/integration/repp/v1/domains/create_test.rb
index ca1c08c5e..bcce43e58 100644
--- a/test/integration/repp/v1/domains/create_test.rb
+++ b/test/integration/repp/v1/domains/create_test.rb
@@ -17,7 +17,7 @@ class ReppV1DomainsCreateTest < ActionDispatch::IntegrationTest
     payload = {
       domain: {
         name: 'domeener.test',
-        registrant_id: contact.code,
+        registrant: contact.code,
         period: 1,
         period_unit: 'y'
       }
@@ -39,7 +39,7 @@ class ReppV1DomainsCreateTest < ActionDispatch::IntegrationTest
     payload = {
       domain: {
         name: 'domeener.test',
-        registrant_id: contact.code,
+        registrant: contact.code,
         period: 3,
         period_unit: 'y'
       }
@@ -61,7 +61,7 @@ class ReppV1DomainsCreateTest < ActionDispatch::IntegrationTest
     payload = {
       domain: {
         name: 'domeener.test',
-        registrant_id: contact.code,
+        registrant: contact.code,
         period: 1,
         period_unit: 'y',
         nameservers_attributes: [
@@ -91,7 +91,7 @@ class ReppV1DomainsCreateTest < ActionDispatch::IntegrationTest
     payload = {
       domain: {
         name: 'domeener.test',
-        registrant_id: contact.code,
+        registrant: contact.code,
         period: 1,
         period_unit: 'y',
         admin_contacts: [ admin_contact.code ],