Try moving everything around

apps/podinfo/podinfo-kustomization.yaml

@@ -0,0 +1,17 @@
+---
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  interval: 30m0s
+  path: ./kustomize
+  prune: true
+  retryInterval: 2m0s
+  sourceRef:
+    kind: GitRepository
+    name: podinfo
+  targetNamespace: default
+  timeout: 3m0s
+  wait: true

apps/podinfo/podinfo-source.yaml

@@ -0,0 +1,11 @@
+---
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  interval: 1m0s
+  ref:
+    branch: master
+  url: https://github.com/stefanprodan/podinfo