ERR_NGROK_2213: Failed to parse configuration for PHASE add-headers: contained an invalid template: TEMPLATE: ERR - ngrok documentation

What does ERR_NGROK_2213 mean?

ngrok returns ERR_NGROK_2213 with this message:

Failed to parse configuration for <PHASE> add-headers: contained an invalid template: <TEMPLATE>: <ERR>.

Where can I get more help with ERR_NGROK_2213?

Email support@ngrok.com and include the error code.