Gateway Error & Update App Button is not visible

Hello Team, I have been getting error as "There was a data source access error. Please contact the gateway administrator". The administrator has created a new data source for same tabular model even though it not working.

meanwhile, I could not update app once I published my report into workspace even If I manually added content and tried to update app. The button has been greyed out or throwing error as Failed to Update an App.

Could you please help me on this.