You do not "turn on" Platform Edition. The Salesforce Platform license arrives in your org once it is on your contract, and an admin assigns it to a user, then grants object access through a profile or permission set. Here is the path in Setup.
- Confirm the license is in your org
In Setup, open Company Information and check Salesforce Platform appears under user licenses with seats available. If it is not there, it is not yet on your contract.
- Create or edit the user
Go to Setup, then Users, and open or create the user. Set the User License field to Salesforce Platform, which then filters the profiles you can choose.
- Assign a compatible profile
Choose a profile built for the Platform license. Clone the standard Platform profile if you need custom defaults rather than editing the original.
- Grant custom object and app access
Use a permission set to give read, create, edit, and delete on your custom objects, plus access to the custom app, then assign that permission set to the user.
On the user record, set User License to Salesforce Platform. This is the value behind Lightning Platform Starter and Plus, and it gates which standard objects the user can ever see.
Pick a profile compatible with the Platform license, for example a cloned Standard Platform User profile, to set the baseline object and field permissions.
Layer a permission set to grant access to your custom objects, Apex classes, and apps without editing the profile for everyone.
Within the profile or permission set, enable read, create, edit, and delete on the custom objects the user needs, staying inside the license object limit.
- You cannot grant a Platform user access to Opportunities, Leads, or Quotes through any profile or permission set. Those objects are excluded at the license level.
- Starter caps custom objects at ten per license and Plus at one hundred and ten. Assigning the wrong tier shows up as a hard wall when you try to deploy more.
- Platform licenses are for internal employees and contractors only. Do not use them to give partners or customers access. Use Experience Cloud licenses for external audiences.