diff --git a/pkg/plugins/datadog/cmd/main/main.go b/pkg/plugins/datadog/cmd/main/main.go
index 8720750..c0ab27e 100644
--- a/pkg/plugins/datadog/cmd/main/main.go
+++ b/pkg/plugins/datadog/cmd/main/main.go
@@ -233,7 +233,10 @@ func (d *DatadogCostSource) getDDCostsForWindow(window opencost.Window, listPric
 				}
 			}
 		}
-		if resp.Meta != nil && resp.Meta.Pagination != nil && resp.Meta.Pagination.NextRecordId.IsSet() {
+		// NextRecordId is a NullableString: IsSet() is true even when the API
+		// returned an explicit JSON null (end of pagination), in which case
+		// Get() returns nil. Guard against that to avoid a SIGSEGV (#68).
+		if resp.Meta != nil && resp.Meta.Pagination != nil && resp.Meta.Pagination.NextRecordId.IsSet() && resp.Meta.Pagination.NextRecordId.Get() != nil {
 			nextPageId = *resp.Meta.Pagination.NextRecordId.Get()
 		} else {
 			nextPageId = ""
@@ -468,6 +471,16 @@ func getDatadogClients(config datadogplugin.DatadogConfig) (context.Context, *da
 	)
 
 	configuration := datadog.NewConfiguration()
+	// The generated client serializes the billable-summary `month` parameter
+	// as a full RFC3339 timestamp, which the Datadog API rejects with
+	// 400 "month must be in the format YYYY-MM". Rewrite it in transit.
+	var baseTransport _nethttp.RoundTripper = _nethttp.DefaultTransport
+	if configuration.HTTPClient != nil && configuration.HTTPClient.Transport != nil {
+		baseTransport = configuration.HTTPClient.Transport
+	}
+	configuration.HTTPClient = &_nethttp.Client{
+		Transport: datadogplugin.MonthParamRoundTripper{Next: baseTransport},
+	}
 	apiClient := datadog.NewAPIClient(configuration)
 	usageAPI := datadogV2.NewUsageMeteringApi(apiClient)
 	v1UsageAPI := datadogV1.NewUsageMeteringApi(apiClient)
diff --git a/pkg/plugins/datadog/datadogplugin/transport.go b/pkg/plugins/datadog/datadogplugin/transport.go
new file mode 100644
index 0000000..9769ef2
--- /dev/null
+++ b/pkg/plugins/datadog/datadogplugin/transport.go
@@ -0,0 +1,45 @@
+package datadog
+
+import (
+	"net/http"
+	"strings"
+	"time"
+)
+
+// billableSummaryPath is the API path whose `month` query parameter requires
+// YYYY-MM formatting.
+const billableSummaryPath = "/api/v1/usage/billable-summary"
+
+// MonthParamRoundTripper rewrites the `month` query parameter on
+// /api/v1/usage/billable-summary requests from the RFC3339 timestamp the
+// generated datadog-api-client-go emits (e.g. 2024-03-01T00:00:00Z) to the
+// YYYY-MM format the Datadog API requires. Without this rewrite the API
+// rejects every request with:
+//
+//	400 Bad Request: {"errors":[{"status":"400","title":"Bad Request",
+//	  "detail":"month must be in the format YYYY-MM"}]}
+//
+// which causes GetDDUnitPrices, and therefore every GetCustomCosts window,
+// to fail.
+type MonthParamRoundTripper struct {
+	// Next is the underlying RoundTripper to delegate to. If nil,
+	// http.DefaultTransport is used.
+	Next http.RoundTripper
+}
+
+func (m MonthParamRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	if strings.HasSuffix(req.URL.Path, billableSummaryPath) {
+		q := req.URL.Query()
+		if month := q.Get("month"); month != "" {
+			if t, err := time.Parse(time.RFC3339, month); err == nil {
+				q.Set("month", t.UTC().Format("2006-01"))
+				req.URL.RawQuery = q.Encode()
+			}
+		}
+	}
+	next := m.Next
+	if next == nil {
+		next = http.DefaultTransport
+	}
+	return next.RoundTrip(req)
+}
diff --git a/pkg/plugins/datadog/datadogplugin/transport_test.go b/pkg/plugins/datadog/datadogplugin/transport_test.go
new file mode 100644
index 0000000..070cb42
--- /dev/null
+++ b/pkg/plugins/datadog/datadogplugin/transport_test.go
@@ -0,0 +1,54 @@
+package datadog
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func doRoundTrip(t *testing.T, path, rawQuery string) string {
+	t.Helper()
+
+	var gotMonth string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotMonth = r.URL.Query().Get("month")
+	}))
+	defer server.Close()
+
+	req, err := http.NewRequest(http.MethodGet, server.URL+path+"?"+rawQuery, nil)
+	if err != nil {
+		t.Fatalf("building request: %v", err)
+	}
+
+	client := &http.Client{Transport: MonthParamRoundTripper{}}
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("round trip: %v", err)
+	}
+	resp.Body.Close()
+
+	return gotMonth
+}
+
+func TestMonthParamRewrittenOnBillableSummary(t *testing.T) {
+	got := doRoundTrip(t, "/api/v1/usage/billable-summary", "month=2024-03-01T00%3A00%3A00Z")
+	if got != "2024-03" {
+		t.Fatalf("expected month=2024-03, got month=%s", got)
+	}
+}
+
+func TestMonthAlreadyShortFormPassedThrough(t *testing.T) {
+	// If the client library starts emitting YYYY-MM itself, the rewrite must
+	// be a no-op rather than corrupting the value.
+	got := doRoundTrip(t, "/api/v1/usage/billable-summary", "month=2024-03")
+	if got != "2024-03" {
+		t.Fatalf("expected month=2024-03, got month=%s", got)
+	}
+}
+
+func TestOtherEndpointsUntouched(t *testing.T) {
+	got := doRoundTrip(t, "/api/v2/usage/hourly_usage", "month=2024-03-01T00%3A00%3A00Z")
+	if got != "2024-03-01T00:00:00Z" {
+		t.Fatalf("expected month unchanged, got month=%s", got)
+	}
+}