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.
- Log into your Google Play Account as account-owner
- Go to "Settings" → "API access"
- Create a new API project or connect an existing one
- CAUTION, if a linked project already exists, please do not change anything, otherwise the current project will be deleted.
- If you already own a project please continue with step 4 and create a Service account
- In "Service Accounts" please press the button "Create service account"
- Within the first section please use the link to get to the overview of the service accounts of you API projects
- In the top menuplease click "Create service account"
- Fill in name and description and click Create
- Project → add Viewer Rolle (source: https://stackoverflow.com/a/54717925) and click continue
- With Create key please generate a key and slect json as format type
- It starts a download of the JSON file, save it and keep it safe.
- Close with Done and close tab
- In the Google Play Store within the popup of "Create service account" please click done
- The service account should now be listed
- Please click "Grant Access" within the service accounts section
- Within the screen Add a new user set the permissions as displayed in the screenshot below and "Adduser"
- head back to "API access" – within the service account section the "View permissions" Link should be displayed
- Navigate to the Team section in the Purple DS Manager and click on settings on the right side of the screen.
- Upload the JSON-file in the team settings section by clicking select file:
- 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)
- otherwise the linked account will not be active