Before getting the answer, please read the following things.

How can I enable a feature on a plan and disable it on another plan?

1. Go to Listing Plans -> Your Plan
2. Select enable / disable status
3. Finally, click Save Changes or Publish button

How can I hide disable feature on Add Listing page?

1. Go to Appearance -> Theme Options
2. Navigate to Add Listing General Settings
3. Set It should not show on Add Listing page option to Unchecked features will

So, if you see a grey field on your Add Listing page, which means:

1. This field is disabled on the current Listing Plan that you are using
2. You are using Show on Add Listing page, but it will be disabled option mode on Theme Options setting

To resolve it:

1. You can re-enable this feature on the Listing Plan
2. Or select the second option on the Theme Options