Script to create a plan from query

[piranha]

I'm writing a shell script to create a plan from query and got to the following curl command:

echo "$PLAN" | curl -s -w '%{redirect_url}' --data-urlencode plan@- -X POST 'https://explain.dalibo.com/new'

It returns an url to the plan, but then the url returns error 500. It's https://explain.dalibo.com/plan/0424...hacb (I can post full URL if you want, but I suppose you can see that in logs somewhere). Any pointers on what's wrong the the query? $PLAN in question is a JSON from postgres.