Hello Mykola,

Hope you're doing well.

Is this error happening for a single application or for all of them?

This is a very strange behavior, usually that error - the underlying connection was closed - occurs when the app pool recycles / craches and the web request is terminated.

Assuming you're working on a prem infrastructure, did you check the platform's connectivity to MABS web service in the Environment Health? Just as a sanity check, since the error would be different if it was a connection problem.

Did you look at your App Pools and IIS Logs?

I truly think your best option is to open a support case and ask OutSystems for some assistance. If you do please do let us know how did you manage to solve this.

Kind regards,

Rui Barradas

+Addition 

Make sure your front-end servers can reach MABS (especially if you're on-prem). 

https://success.outsystems.com/documentation/11/setup_outsystems_infrastructure_and_platform/setting_up_outsystems/outsystems_network_requirements/meeting_mobile_apps_build_service_connectivity_requirements/

Good luck

I've encountered a similar issue before, and I found the detailed error logs in the Lifetime Server Service Center.

Hi @Mykola (Nick) Tkachenko , 

I think you can also check at the Front-end environment browser after clicking on https://nativebuilder.api.outsystems.com/ , the expected message is "Missing Authentication Token" 

if you retrieved something different from this,

1. if port 443 is open as per our Network Requirements? 
2. Are there any Application Load Balancers, firewalls, VPNs, or antivirus that could be blocking the connection to the service?

Restarting deployment server and refreshing all references again for all producer modules solved the problem. It was only one app with the issue.