diff --git a/security/acme-client/pkg-descr b/security/acme-client/pkg-descr
index be9ada2d6..0f08eea38 100644
--- a/security/acme-client/pkg-descr
+++ b/security/acme-client/pkg-descr
@@ -16,6 +16,7 @@ Added:
 * add support for Zone.eu DNS API (#2417)
 * add support for Njalla DNS API (#2446)
 * add support for Domeneshop DNS API (#2390)
+* add support for IONOS domain API (#2345)
 
 Fixed:
 * sftp update of write protected cert files with a numeric owner (#2426)
diff --git a/security/acme-client/src/opnsense/mvc/app/controllers/OPNsense/AcmeClient/forms/dialogValidation.xml b/security/acme-client/src/opnsense/mvc/app/controllers/OPNsense/AcmeClient/forms/dialogValidation.xml
index 6fac8e3b5..527601cfd 100644
--- a/security/acme-client/src/opnsense/mvc/app/controllers/OPNsense/AcmeClient/forms/dialogValidation.xml
+++ b/security/acme-client/src/opnsense/mvc/app/controllers/OPNsense/AcmeClient/forms/dialogValidation.xml
@@ -550,6 +550,21 @@
         <label>Password</label>
         <type>password</type>
     </field>
+    <field>
+        <label>IONOS domain API</label>
+        <type>header</type>
+        <style>table_dns table_dns_ionos</style>
+    </field>
+    <field>
+        <id>validation.dns_ionos_prefix</id>
+        <label>Prefix</label>
+        <type>text</type>
+    </field>
+    <field>
+        <id>validation.dns_ionos_secret</id>
+        <label>Secret</label>
+        <type>password</type>
+    </field>
     <field>
         <label>IPSConfig</label>
         <type>header</type>
diff --git a/security/acme-client/src/opnsense/mvc/app/library/OPNsense/AcmeClient/LeValidation/DnsIonos.php b/security/acme-client/src/opnsense/mvc/app/library/OPNsense/AcmeClient/LeValidation/DnsIonos.php
new file mode 100644
index 000000000..19d1b5190
--- /dev/null
+++ b/security/acme-client/src/opnsense/mvc/app/library/OPNsense/AcmeClient/LeValidation/DnsIonos.php
@@ -0,0 +1,45 @@
+<?php
+
+/*
+ * Copyright (C) 2021 Frank Wall
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
+ * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+namespace OPNsense\AcmeClient\LeValidation;
+
+use OPNsense\AcmeClient\LeValidationInterface;
+use OPNsense\Core\Config;
+
+/**
+ * IONOS API
+ * @package OPNsense\AcmeClient
+ */
+class DnsIonos extends Base implements LeValidationInterface
+{
+    public function prepare()
+    {
+        $this->acme_env['IONOS_PREFIX'] = (string)$this->config->dns_ionos_prefix;
+        $this->acme_env['IONOS_SECRET'] = (string)$this->config->dns_ionos_secret;
+    }
+}
diff --git a/security/acme-client/src/opnsense/mvc/app/models/OPNsense/AcmeClient/AcmeClient.xml b/security/acme-client/src/opnsense/mvc/app/models/OPNsense/AcmeClient/AcmeClient.xml
index 1f3db5fd0..70e5080e7 100644
--- a/security/acme-client/src/opnsense/mvc/app/models/OPNsense/AcmeClient/AcmeClient.xml
+++ b/security/acme-client/src/opnsense/mvc/app/models/OPNsense/AcmeClient/AcmeClient.xml
@@ -409,6 +409,7 @@
                         <dns_infoblox>Infoblox API</dns_infoblox>
                         <dns_infomaniak>Infomaniak API</dns_infomaniak>
                         <dns_inwx>INWX XMLRPC API</dns_inwx>
+                        <dns_ionos>IONOS domain API</dns_ionos>
                         <dns_ispconfig>ISPConfig 3.1+ API</dns_ispconfig>
                         <dns_joker>Joker API</dns_joker>
                         <dns_kinghost>KingHost DNS API</dns_kinghost>
@@ -621,6 +622,12 @@
                 <dns_inws_password type="TextField">
                     <Required>N</Required>
                 </dns_inws_password>
+                <dns_ionos_prefix type="TextField">
+                    <Required>N</Required>
+                </dns_ionos_prefix>
+                <dns_ionos_secret type="TextField">
+                    <Required>N</Required>
+                </dns_ionos_secret>
                 <dns_ispconfig_user type="TextField">
                     <Required>N</Required>
                 </dns_ispconfig_user>