Deployment fails with error "manifest for liferay/dxp:7.3-u6 not found: manifest unknown"

Note: please note that Liferay has renamed its Liferay Experience Could offerings to Liferay SaaS (formerly LXC) and Liferay PaaS (formerly LXC-SM).

Issue

• I'm trying to deploy the liferay service but the process fails.
• The Build logs show this error:

  Step #1: manifest for liferay/dxp:7.3-u6 not found: manifest unknown: manifest unknown

Environment

• Liferay PaaS

Resolution

• This error message tells us that there is no liferay application image like liferay/dxp:7.3-u6.
• Please use in the liferay.workspace.docker.image.liferay property inside of the gradle.properties file an application image found in our repository: /r/liferay/dxp.
• For this particular case, the correct liferay image is: liferay/dxp:7.3.10-u6.

Additional Information

• How can I find valid Workspace Product Keys to configure for liferay.workspace.product in gradle.property?