I guess one option is to try to run a curl query to update the deSEC side using a crontab and log the results periodically? Not sure how we can debug an external service. All we get is the 502 unless you have better suggestions.
From the upstream forum, you use cron(1) to trigger the checks, randomise the time. ~/5 * * * * would choose a random 5 minute interval for example. So it might run at …:07:00, …:12:00, … instead of …:05:00, …:10:00, etc . AFAIK, this is already the case with Cloudron's crontab.