diff --git a/HISTORY.rst b/HISTORY.rst
index 4a6bc22..f707936 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -3,6 +3,14 @@
 History
 -------
 
+2.11.0
++++++++++++++++++++
+
+* Updated the validation for the Report Transactions API to make the
+  ``ip_address`` parameter optional. Now the ``tag`` and at least one of the
+  following parameters must be supplied: ``ip_address``, ``maxmind_id``,
+  ``minfraud_id``, ``transaction_id``.
+
 2.10.0 (2024-04-16)
 +++++++++++++++++++
 
diff --git a/README.rst b/README.rst
index e4b8bc2..144761d 100644
--- a/README.rst
+++ b/README.rst
@@ -98,7 +98,8 @@ The method takes a dictionary representing the report to be sent to the web
 service. The structure of this dictionary should be in `the format specified
 in the REST API documentation
 <https://dev.maxmind.com/minfraud/report-a-transaction?lang=en>`__. The
-``ip_address`` and ``tag`` fields are required. All other fields are optional.
+required fields are ``tag`` and one or more of the following: ``ip_address``,
+``maxmind_id``, ``minfraud_id``, ``transaction_id``.
 
 Request Validation (for all request methods)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/minfraud/validation.py b/minfraud/validation.py
index 7116787..296b660 100644
--- a/minfraud/validation.py
+++ b/minfraud/validation.py
@@ -379,14 +379,33 @@ def _uuid(s: str) -> str:
     raise ValueError
 
 
-validate_report = Schema(
+def _transaction_id(s: Optional[str]) -> str:
+    if isinstance(s, str) and len(s) > 0:
+        return s
+    raise ValueError
+
+
+validate_report_schema = Schema(
     {
         "chargeback_code": str,
-        Required("ip_address"): _ip_address,
+        "ip_address": _ip_address,
         "maxmind_id": _maxmind_id,
         "minfraud_id": _uuid,
         "notes": str,
         Required("tag"): _tag,
-        "transaction_id": str,
+        "transaction_id": _transaction_id,
     },
 )
+
+
+def validate_at_least_one_identifier_field(report):
+    optional_fields = ["ip_address", "maxmind_id", "minfraud_id", "transaction_id"]
+    if not any(field in report for field in optional_fields):
+        raise ValueError("The report must contain at least one of the following fields: 'ip_address', 'maxmind_id', 'minfraud_id', 'transaction_id'.")
+    return True
+
+
+def validate_report(report):
+    validate_report_schema(report)
+    validate_at_least_one_identifier_field(report)
+    return True
diff --git a/tests/test_validation.py b/tests/test_validation.py
index 62a8953..87084ae 100644
--- a/tests/test_validation.py
+++ b/tests/test_validation.py
@@ -51,11 +51,17 @@ def setup_report(self, report):
 
     def check_invalid_report(self, report):
         self.setup_report(report)
+        self.check_invalid_report_no_setup(report)
+
+    def check_invalid_report_no_setup(self, report):
         with self.assertRaises(MultipleInvalid, msg=f"{report} is invalid"):
             validate_report(report)
 
     def check_report(self, report):
         self.setup_report(report)
+        self.check_report_no_setup(report)
+
+    def check_report_no_setup(self, report):
         try:
             validate_report(report)
         except MultipleInvalid as e:
@@ -431,3 +437,9 @@ def test_tag(self):
             self.check_report({"tag": good})
         for bad in ("risky_business", "", None):
             self.check_invalid_report({"tag": bad})
+
+    def test_report_valid_identifier(self):
+        self.check_report_no_setup({"tag": "chargeback", "ip_address": "1.1.1.1"})
+        self.check_report_no_setup({"tag": "chargeback", "minfraud_id": "58fa38d8-4b87-458b-a22b-f00eda1aa20d"})
+        self.check_report_no_setup({"tag": "chargeback", "maxmind_id": "12345678"})
+        self.check_report_no_setup({"tag": "chargeback", "transaction_id": "abc123"})