diff --git a/README.md b/README.md
index c5400d8..8d68d01 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,8 @@ Unlike `vatExempt`, this package does **not** expect `unitPrice` to be de-grosse
 - Visual PDF (`invoicePdf.tsx`/`correctionInvoicePdf.tsx`): the "enthält X% MwSt." annotation under Gesamt becomes "Gemäß § 19 UStG wird keine Umsatzsteuer berechnet." instead — takes precedence over the `vatExempt` note if (implausibly) both were ever set.
 - E-invoice XML (`buildEInvoiceData.ts`): VAT category `E` + a free-text exemption reason, no VATEX code — see "E-invoicing" above.
 
+`InvoiceSeller.vatId` is now optional (`string | null`, was a plain required `string`) for the same reason — a Kleinunternehmer commonly never registers for an USt-IdNr. at all (no intra-EU trade). Every renderer treats a missing value as "omit the USt-IdNr. line/field" rather than printing an empty one: the visual PDF footer drops the whole `· USt-IdNr. …` segment, and `buildEInvoiceData.ts`'s `sellerParty()` omits `cac:PartyTaxScheme` entirely rather than emitting one with a blank `CompanyID`.
+
 ## CI validation (Mustang)
 
 Every push/PR runs `.gitea/workflows/validate-einvoice.yml` against git.mk360.de's own self-hosted Gitea Actions runner (`vps-runner`, registered on the same VPS as Gitea/Payload — see `/home/marco/dev/docker/docker-compose.yml`'s `act_runner` service):
diff --git a/package.json b/package.json
index 435b9aa..e1db368 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@einfach-produktiv/invoicing",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "private": true,
   "description": "Shared invoice / correction-invoice (Stornorechnung, Gutschrift) PDF generation and VAT-breakdown math, consumed as a git dependency by both the einfach-produktiv frontend and the payload backend — not published to npm.",
   "type": "module",
diff --git a/src/correctionInvoicePdf.tsx b/src/correctionInvoicePdf.tsx
index c52af08..4c6b833 100644
--- a/src/correctionInvoicePdf.tsx
+++ b/src/correctionInvoicePdf.tsx
@@ -379,8 +379,10 @@ function CorrectionInvoiceDocument({ kind, order, seller }: { kind: CorrectionIn
 
         <View style={styles.footer} fixed>
           <Text>
-            {seller.sellerName} · {seller.sellerStreet}, {seller.sellerZip} {seller.sellerCity} · {seller.sellerEmail} · USt-IdNr.{" "}
-            {seller.vatId}
+            {seller.sellerName} · {seller.sellerStreet}, {seller.sellerZip} {seller.sellerCity} · {seller.sellerEmail}
+            {/* Same "omit entirely when unset" as invoicePdf.tsx's own
+                footer — see seller.ts's own comment on vatId. */}
+            {seller.vatId ? ` · USt-IdNr. ${seller.vatId}` : ""}
             {seller.registerCourt && seller.registerNumber ? ` · ${seller.registerCourt} · ${seller.registerNumber}` : ""}
             {seller.managingDirector ? ` · Geschäftsführung: ${seller.managingDirector}` : ""}
           </Text>
diff --git a/src/einvoice/buildEInvoiceData.ts b/src/einvoice/buildEInvoiceData.ts
index ddcb8d9..7ec54a6 100644
--- a/src/einvoice/buildEInvoiceData.ts
+++ b/src/einvoice/buildEInvoiceData.ts
@@ -185,12 +185,21 @@ function sellerParty(seller: InvoiceSeller): UblInvoice["cac:AccountingSupplierP
         "cbc:PostalZone": seller.sellerZip,
         "cac:Country": { "cbc:IdentificationCode": countryCode(seller.sellerCountry) as SellerCountryCode },
       },
-      "cac:PartyTaxScheme": [
-        {
-          "cbc:CompanyID": seller.vatId,
-          "cac:TaxScheme": { "cbc:ID": "VAT" },
-        },
-      ],
+      // Omitted entirely (not a PartyTaxScheme with an empty CompanyID)
+      // when unset — a Kleinunternehmer (§19 UStG) often has no USt-IdNr.
+      // at all, see seller.ts's own comment. Same "always present in this
+      // shop's real production data today, but must degrade safely" spirit
+      // as paymentMeans()'s own `!seller.iban` check above.
+      ...(seller.vatId
+        ? {
+            "cac:PartyTaxScheme": [
+              {
+                "cbc:CompanyID": seller.vatId,
+                "cac:TaxScheme": { "cbc:ID": "VAT" },
+              },
+            ],
+          }
+        : {}),
       "cac:PartyLegalEntity": { "cbc:RegistrationName": seller.sellerName },
       "cac:Contact": { "cbc:ElectronicMail": seller.sellerEmail },
     },
diff --git a/src/invoicePdf.tsx b/src/invoicePdf.tsx
index 1139de5..60ab31c 100644
--- a/src/invoicePdf.tsx
+++ b/src/invoicePdf.tsx
@@ -449,8 +449,11 @@ export function InvoiceDocument({ order, seller }: { order: InvoiceOrder; seller
 
         <View style={styles.footer} fixed>
           <Text>
-            {seller.sellerName} · {seller.sellerStreet}, {seller.sellerZip} {seller.sellerCity} · {seller.sellerEmail} · USt-IdNr.{" "}
-            {seller.vatId}
+            {seller.sellerName} · {seller.sellerStreet}, {seller.sellerZip} {seller.sellerCity} · {seller.sellerEmail}
+            {/* Omitted entirely (not "USt-IdNr. " with a blank value) when
+                unset — a Kleinunternehmer (§19 UStG) often has no USt-IdNr.
+                at all, see seller.ts's own comment. */}
+            {seller.vatId ? ` · USt-IdNr. ${seller.vatId}` : ""}
             {seller.registerCourt && seller.registerNumber ? ` · ${seller.registerCourt} · ${seller.registerNumber}` : ""}
             {seller.managingDirector ? ` · Geschäftsführung: ${seller.managingDirector}` : ""}
           </Text>
diff --git a/src/seller.ts b/src/seller.ts
index 4a2e90d..c7442a9 100644
--- a/src/seller.ts
+++ b/src/seller.ts
@@ -9,7 +9,14 @@ export type InvoiceSeller = {
   sellerCity: string;
   sellerCountry: string;
   sellerEmail: string;
-  vatId: string;
+  // Optional as of the Kleinunternehmerregelung (§19 UStG) addition — a
+  // Kleinunternehmer often only has a Steuernummer, never registers for an
+  // USt-IdNr. at all (no intra-EU trade), so company-settings.vatId is no
+  // longer a hard-required field on the Payload side (see that
+  // collection's own comment). Every renderer here already treats a
+  // missing vatId as "omit the USt-IdNr. line/field" rather than printing
+  // an empty value.
+  vatId?: string | null;
   taxRatePercent: number;
   // Structured (Phase 2 of the e-invoicing migration — EN16931 wants
   // discrete PaymentMeans data, not a free-text paragraph a human