We are facing an error in the deploy of Regclient, in kubernetes.
As from my previous experience in your setup you are setting http and https proxy for each deployment. Please correct me if I am wrong.
Basically we are connecting to timestamp.comodoca.com from reg-client downloader for timestamping the signed MOSIP jars.
In case proxy is not enabled, enabling the same will solve the 503 error you are getting while timestamping the MOSIP jars.
Please give it a try and confirm us back.