In the PRINCE2 methodology, the 'project mandate' is the term used for initial documentation that triggers the start of a project, typically provided by corporate or program management. It can often come in the form of a request for proposal received by an external supplier, setting out the initial definition of the project and what it aims to achieve, which then leads to more detailed project definitions in the 'starting up a project' process.
References: PRINCE27 Foundation resources on project initiation documentation.

The objectives of the 'Starting Up a Project' process include providing an interface between the corporate or program environment and the project (objective 1) and providing business justification for initiating the project (objective 4). This process ensures that the project is viable and worthwhile before further resources are committed and that there is a clear link to corporate strategies and ongoing work.References:
(PRINCE2 7 Foundation Handbook, AXELOS)

In PRINCE2, issue management and change control are closely related, where issue management is considered a subset of change control. Change control is a broader process that encompasses all aspects of managing changes within the project, including issues that might impact the project's scope, timescales, costs, or quality. Issue management specifically deals with resolving issues that can affect the progress of the project.
References: (PRINCE27 Foundation Handbook, AXELOS)

Section: Volume A
Explanation/Reference: