Microsoft.Crm.CrmException: Property ‘x’ isn’t declared on the control manifest in Microsoft Dynamics 365

We got this error while trying to save the form which uses the PCF Control.

This was because the name of the property was changed

And the updated solution was imported, while the control on the form was still referring to the old property name.

Fix is straightforward, remove the field using that control with old property name from the form and save the change.

Hope it helps..