Seeking suggestions on location of the implementation of REST client APIs

We have an application whose simplified block diagram is shown in the below image.

Currently, when the user performs some GUI actions, through path (A), middle layer will be configured, using C++ API. Also, REST API(s) will be called through path (D) to save the settings.

When the application starts, Middle Layer reads the settings from DB through path (B) and configures.

Is it right to have REST calls from GUI directly through (D) or it should be moved to Middle Layer? Please suggest.