With the update to the Google Play API version 3 the following process has to be done in the respective playstores until 01.12.2019, so that in-app purchases can be validated without problems.

  1. Log into your Google Play Account as  account-owner
  2. Go to "Settings" → "API access"
  3. Create a new API project or connect an existing one
    1. CAUTION, if a linked project already exists, please do not change anything, otherwise the current project will be deleted.
    2. If you already own a project please continue with step 4 and create a Service account
  4. In "Service Accounts" please press the button "Create service account"
  5. Within the first section please use the link to get to the overview of the service accounts of you API projects
  6. In the top menuplease click "Create service account"
  7. Fill in name and description and click Create
  8. Project → add Viewer Rolle (source: https://stackoverflow.com/a/54717925) and click continue
  9. With Create key please generate a key and slect json as format type
  10. It starts a download of the JSON file, save it and keep it safe.
  11. Close with Done and close tab
  12. In the  Google Play Store within the popup of "Create service account" please click done
  13. The service account should now be listed
  14. Please click "Grant Access" within the service accounts section
  15. Within the screen Add a new user set the permissions as displayed in the screenshot below and "Adduser"
  16. head back to "API access" – within the service account section the "View permissions" Link should be displayed
  17. Navigate to the Team section in the Purple DS Manager and click on settings on the right side of the screen.
  18. Upload the JSON-file in the team settings section by clicking select file:
  19. Update an existing product in the Play Store (no changes necessary, just save) or create a new product (source: https://stackoverflow.com/a/25497513/381899)
    1. otherwise the linked account will not be active