My skill generated an imagePDF but nothing was sent

Outbound attachments from the agent must include a MEDIA:<path-or-url> line (on its own line). See OpenClaw assistant setup and Agent send.
CLI sending:
openclaw message send --target +15555550123 --message "Here you go" --media /path/to/file.png
Also check:
The target channel supports outbound media and isn’t blocked by allowlists.
The file is within the provider’s size limits (images are resized to max 2048px).
See Images.