diff --git a/__tests__/actions/auth.js b/__tests__/actions/auth.js
index eff03f17..2922e0b4 100644
--- a/__tests__/actions/auth.js
+++ b/__tests__/actions/auth.js
@@ -1,17 +1,16 @@
-const MOCK_GROUPS_REQ_URL = 'https://api.topcoder-dev.com/v3/groups?memberId=12345&membershipType=user';
-const MOCK_PROFILE_REQ_URL = 'https://api.topcoder-dev.com/v3/members/username12345';
+const MOCK_GROUPS_REQ_URL = 'https://api.topcoder-dev.com/v5/groups?memberId=12345&membershipType=user';
+const MOCK_PROFILE_REQ_URL = 'https://api.topcoder-dev.com/v5/members/username12345';
 
 jest.mock('isomorphic-fetch', () => jest.fn(url => Promise.resolve({
+  ok: true,
   json: () => {
     let content;
     switch (url) {
       case MOCK_GROUPS_REQ_URL: content = ['Group1', 'Group2']; break;
-      case MOCK_PROFILE_REQ_URL: content = { userId: 12345 }; break;
+      case MOCK_PROFILE_REQ_URL: content = [{ userId: 12345 }]; break;
       default: throw new Error('Unexpected URL!');
     }
-    return {
-      result: { content, status: 200 },
-    };
+    return content;
   },
 })));
 
diff --git a/config/test.js b/config/test.js
index add8c31c..1d2ca856 100644
--- a/config/test.js
+++ b/config/test.js
@@ -2,6 +2,7 @@ module.exports = {
   API: {
     V2: 'https://api.topcoder-dev.com/v2',
     V3: 'https://api.topcoder-dev.com/v3',
+    V5: 'https://api.topcoder-dev.com/v5',
   },
   dummyConfigKey: 'Dummy config value',
   SECRET: {
diff --git a/src/actions/auth.js b/src/actions/auth.js
index c585ec71..0a611f43 100644
--- a/src/actions/auth.js
+++ b/src/actions/auth.js
@@ -9,19 +9,21 @@ import { getApi } from '../services/api';
 
 /**
  * @static
- * @desc Creates an action that loads Topcoder user profile from v3 API.
+ * @desc Creates an action that loads Topcoder user profile from v5 API.
  * @param {String} userTokenV3 v3 authentication token.
  * @return {Action}
  */
 function loadProfileDone(userTokenV3) {
   if (!userTokenV3) return Promise.resolve(null);
   const user = decodeToken(userTokenV3);
-  const api = getApi('V3', userTokenV3);
+  const api = getApi('V5', userTokenV3);
   return Promise.all([
     api.get(`/members/${user.handle}`)
-      .then(res => res.json()).then(res => (res.result.status === 200 ? res.result.content : {})),
+      .then(res => (res.ok ? res.json() : new Error(res.statusText)))
+      .then(res => (res.message ? new Error(res.message) : res[0])),
     api.get(`/groups?memberId=${user.userId}&membershipType=user`)
-      .then(res => res.json()).then(res => (res.result.status === 200 ? res.result.content : [])),
+      .then(res => (res.ok ? res.json() : new Error(res.statusText)))
+      .then(res => (res.message ? new Error(res.message) : res)),
   ]).then(([profile, groups]) => ({ ...profile, groups }));
 }
 
diff --git a/src/services/__mocks__/challenges.js b/src/services/__mocks__/challenges.js
index 0dc59e7c..2c5e7ae4 100644
--- a/src/services/__mocks__/challenges.js
+++ b/src/services/__mocks__/challenges.js
@@ -85,8 +85,8 @@ export function normalizeChallengeDetails(v3, v3Filtered, v3User, v2, username)
   // Fill missing data from v3_filtered
   if (v3Filtered) {
     const groups = {};
-    if (v3Filtered.groupIds) {
-      v3Filtered.groupIds.forEach((id) => {
+    if (v3Filtered.groups) {
+      v3Filtered.groups.forEach((id) => {
         groups[id] = true;
       });
     }
@@ -165,8 +165,8 @@ export function normalizeChallengeDetails(v3, v3Filtered, v3User, v2, username)
 export function normalizeChallenge(challenge, username) {
   const registrationOpen = challenge.allPhases.filter(d => d.name === 'Registration')[0].isOpen ? 'Yes' : 'No';
   const groups = {};
-  if (challenge.groupIds) {
-    challenge.groupIds.forEach((id) => {
+  if (challenge.groups) {
+    challenge.groups.forEach((id) => {
       groups[id] = true;
     });
   }
diff --git a/src/services/groups.js b/src/services/groups.js
index 69603c0f..a3b42a80 100644
--- a/src/services/groups.js
+++ b/src/services/groups.js
@@ -170,8 +170,8 @@ function mergeGroup(groups, group) {
  * @param {Object} group
  * @return {String[]} Array of IDs.
  */
-export function reduceGroupIds({ oldId, subGroups }) {
-  let res = [oldId];
+export function reduceGroupIds({ id, subGroups }) {
+  let res = [id];
   if (subGroups) {
     subGroups.forEach((g) => {
       res = res.concat(reduceGroupIds(g));
@@ -210,7 +210,7 @@ class GroupService {
    */
   async addMember(groupId, memberId, membershipType) {
     const response = await this.private.api.postJson(`/groups/${groupId}/members`, {
-      param: { memberId, membershipType },
+      memberId, membershipType,
     });
 
     return handleApiResponse(response);
diff --git a/src/utils/challenge/filter.js b/src/utils/challenge/filter.js
index 95b6e18a..ca6de71d 100644
--- a/src/utils/challenge/filter.js
+++ b/src/utils/challenge/filter.js
@@ -18,7 +18,7 @@
  * endDate {Number|String} - Permits only those challenges with submission
  * deadline before this date.
  *
- * groupIds {Array} - Permits only the challenges belonging to at least one
+ * groups {Array} - Permits only the challenges belonging to at least one
  * of the groups which IDs are presented as keys in this object.
  *
  * or {Object[]} - All other filter fields applied to the challenge with AND
@@ -71,8 +71,8 @@ import { COMPETITION_TRACKS, REVIEW_OPPORTUNITY_TYPES } from '../tc';
  */
 
 function filterByGroupIds(challenge, state) {
-  if (!state.groupIds) return true;
-  return state.groupIds.some(id => challenge.groups[id]);
+  if (!state.groups) return true;
+  return state.groups.some(id => challenge.groups[id]);
 }
 
 function filterByRegistrationOpen(challenge, state) {
@@ -343,7 +343,7 @@ export function combine(...filters) {
   const res = {};
   filters.forEach((filter) => {
     combineEndDate(res, filter);
-    combineArrayRules(res, filter, 'groupIds');
+    combineArrayRules(res, filter, 'groups');
     /* TODO: The registrationOpen rule is just ignored for now. */
     combineStartDate(res, filter);
     combineArrayRules(res, filter, 'or', true);
@@ -379,15 +379,8 @@ export function combine(...filters) {
  * @return {Object}
  */
 export function mapToBackend(filter) {
-  if (filter.or) return {};
-
   const res = {};
-  if (filter.groupIds) res.groupIds = filter.groupIds.join(',');
-
-  /* NOTE: Right now the frontend challenge filter by tag works different,
-   * it looks for matches in the challenge name OR in the techs / platforms. */
-  // if (filter.tags) res.technologies = filter.tags.join(',');
-
+  if (filter.groups) res.groups = filter.groups;
   return res;
 }