diff --git a/lib/shared/keyserver-utils.js b/lib/shared/keyserver-utils.js
--- a/lib/shared/keyserver-utils.js
+++ b/lib/shared/keyserver-utils.js
@@ -13,7 +13,7 @@
 
 function useIsKeyserverURLValid(
   keyserverURL?: string,
-): () => Promise<?VersionResponse> {
+): () => Promise<VersionResponse> {
   const urlsToIDs: { +[keyserverID: string]: ?string } =
     useSelector(urlsToIDsSelector);
 
@@ -53,18 +53,14 @@
 
   return React.useCallback(async () => {
     if (!keyserverURL) {
-      return null;
+      throw new Error('isKeyserverURLValid called with empty URL');
     }
 
     const getVersionPromise = getVersionCall();
     void dispatchActionPromise(getVersionActionTypes, getVersionPromise);
 
-    try {
-      const { versionResponses } = await getVersionPromise;
-      return versionResponses[Object.keys(versionResponses)[0]];
-    } catch (e) {
-      return null;
-    }
+    const { versionResponses } = await getVersionPromise;
+    return versionResponses[Object.keys(versionResponses)[0]];
   }, [dispatchActionPromise, getVersionCall, keyserverURL]);
 }
 
diff --git a/native/profile/add-keyserver.react.js b/native/profile/add-keyserver.react.js
--- a/native/profile/add-keyserver.react.js
+++ b/native/profile/add-keyserver.react.js
@@ -8,6 +8,7 @@
 import { useIsKeyserverURLValid } from 'lib/shared/keyserver-utils.js';
 import type { KeyserverInfo } from 'lib/types/keyserver-types.js';
 import { defaultKeyserverInfo } from 'lib/types/keyserver-types.js';
+import { getMessageForException } from 'lib/utils/errors.js';
 import { useDispatch } from 'lib/utils/redux-utils.js';
 
 import type { ProfileNavigationProp } from './profile.react.js';
@@ -16,15 +17,20 @@
 import type { NavigationRoute } from '../navigation/route-names.js';
 import { useSelector } from '../redux/redux-utils.js';
 import { useStyles, useColors } from '../themes/colors.js';
+import { AppOutOfDateAlertDetails } from '../utils/alert-messages.js';
 import { useStaffCanSee } from '../utils/staff-utils.js';
 
 type KeyserverCheckStatus =
   | { +status: 'inactive' }
   | { +status: 'loading' }
-  | { +status: 'error' };
+  | { +status: 'error', +error: 'generic' | 'client_version_unsupported' };
 const keyserverCheckStatusInactive = { status: 'inactive' };
 const keyserverCheckStatusLoading = { status: 'loading' };
-const keyserverCheckStatusError = { status: 'error' };
+const keyserverCheckStatusGenericError = { status: 'error', error: 'generic' };
+const keyserverCheckStatusVersionError = {
+  status: 'error',
+  error: 'client_version_unsupported',
+};
 
 type Props = {
   +navigation: ProfileNavigationProp<'AddKeyserver'>,
@@ -59,9 +65,16 @@
     }
     setStatus(keyserverCheckStatusLoading);
 
-    const keyserverVersionData = await isKeyserverURLValidCallback();
-    if (!keyserverVersionData) {
-      setStatus(keyserverCheckStatusError);
+    let keyserverVersionData;
+    try {
+      keyserverVersionData = await isKeyserverURLValidCallback();
+    } catch (e) {
+      const message = getMessageForException(e);
+      if (message === 'client_version_unsupported') {
+        setStatus(keyserverCheckStatusVersionError);
+      } else {
+        setStatus(keyserverCheckStatusGenericError);
+      }
       return;
     }
     setStatus(keyserverCheckStatusInactive);
@@ -97,19 +110,20 @@
     [],
   );
 
-  const showErrorMessage = status.status === 'error';
+  const { error } = status;
   const errorMessage = React.useMemo(() => {
-    if (!showErrorMessage) {
+    let errorText;
+    if (error === 'client_version_unsupported') {
+      errorText = AppOutOfDateAlertDetails.message;
+    } else if (error) {
+      errorText =
+        'Cannot connect to keyserver. Please check the URL or your ' +
+        'and try again.';
+    } else {
       return null;
     }
-
-    return (
-      <Text style={styles.errorMessage}>
-        Cannot connect to keyserver. Please check the URL or your connection and
-        try again.
-      </Text>
-    );
-  }, [showErrorMessage, styles.errorMessage]);
+    return <Text style={styles.errorMessage}>{errorText}</Text>;
+  }, [error, styles.errorMessage]);
 
   return (
     <View style={styles.container}>
diff --git a/web/modals/keyserver-selection/add-keyserver-modal.react.js b/web/modals/keyserver-selection/add-keyserver-modal.react.js
--- a/web/modals/keyserver-selection/add-keyserver-modal.react.js
+++ b/web/modals/keyserver-selection/add-keyserver-modal.react.js
@@ -7,22 +7,28 @@
 import { useIsKeyserverURLValid } from 'lib/shared/keyserver-utils.js';
 import type { KeyserverInfo } from 'lib/types/keyserver-types.js';
 import { defaultKeyserverInfo } from 'lib/types/keyserver-types.js';
+import { getMessageForException } from 'lib/utils/errors.js';
 import { useDispatch } from 'lib/utils/redux-utils.js';
 
 import css from './add-keyserver-modal.css';
 import Button, { buttonThemes } from '../../components/button.react.js';
 import { useSelector } from '../../redux/redux-utils.js';
 import { useStaffCanSee } from '../../utils/staff-utils.js';
+import { getVersionUnsupportedError } from '../../utils/version-utils.js';
 import Input from '../input.react.js';
 import Modal from '../modal.react.js';
 
 type KeyserverCheckStatus =
   | { +status: 'inactive' }
   | { +status: 'loading' }
-  | { +status: 'error' };
+  | { +status: 'error', +error: 'generic' | 'client_version_unsupported' };
 const keyserverCheckStatusInactive = { status: 'inactive' };
 const keyserverCheckStatusLoading = { status: 'loading' };
-const keyserverCheckStatusError = { status: 'error' };
+const keyserverCheckStatusGenericError = { status: 'error', error: 'generic' };
+const keyserverCheckStatusVersionError = {
+  status: 'error',
+  error: 'client_version_unsupported',
+};
 
 function AddKeyserverModal(): React.Node {
   const { popModal } = useModalContext();
@@ -55,9 +61,16 @@
     }
     setStatus(keyserverCheckStatusLoading);
 
-    const keyserverVersionData = await isKeyserverURLValidCallback();
-    if (!keyserverVersionData) {
-      setStatus(keyserverCheckStatusError);
+    let keyserverVersionData;
+    try {
+      keyserverVersionData = await isKeyserverURLValidCallback();
+    } catch (e) {
+      const message = getMessageForException(e);
+      if (message === 'client_version_unsupported') {
+        setStatus(keyserverCheckStatusVersionError);
+      } else {
+        setStatus(keyserverCheckStatusGenericError);
+      }
       return;
     }
     setStatus(keyserverCheckStatusInactive);
@@ -81,16 +94,18 @@
     isKeyserverURLValidCallback,
   ]);
 
-  const showErrorMessage = status.status === 'error';
+  const { error } = status;
   const errorMessage = React.useMemo(() => {
     let errorText;
-    if (showErrorMessage) {
+    if (error === 'client_version_unsupported') {
+      errorText = getVersionUnsupportedError();
+    } else if (error) {
       errorText =
         'Cannot connect to keyserver. Please check the URL or your ' +
         'connection and try again.';
     }
     return <div className={css.errorMessage}>{errorText}</div>;
-  }, [showErrorMessage]);
+  }, [error]);
 
   const buttonDisabled = !keyserverURL || status.status === 'loading';
   const addKeyserverButton = React.useMemo(