Is this it?

MetaObjects/cert-manager-issuer.yml

@@ -12,5 +12,5 @@ spec:
       - dns01:
           cloudflare:
             apiTokenSecretRef:
-              name: cloudflare-api-token-secret
+              name: cloudflare-api-token
               key: CLOUDFLARE_API_KEY

MetaObjects/ext-store.yml

@@ -2,6 +2,7 @@ apiVersion: external-secrets.io/v1alpha1
 kind: SecretStore
 metadata:
   name: vault-backend
+  namespace: cert-manager
 spec:
   provider:
     vault:
@@ -17,14 +18,15 @@ apiVersion: external-secrets.io/v1alpha1
 kind: ExternalSecret
 metadata:
   name: vault-example
+  namespace: cert-manager
 spec:
   secretStoreRef:
     name: vault-backend
     kind: SecretStore
   target:
-    name: my-thing
+    name: cloudflare-api-token
   data:
-    - secretKey: foobar
+    - secretKey: CLOUDFLARE_API_KEY
       remoteRef:
         key: cloudflare-api-token-secret
         property: CLOUDFLARE_API_KEY