No, we don't at the moment provide such an example, or ( to my knowledge) plan to provide it.
The letter of support should e.g. state that the municipality is informed about your planned experiment and any sensors you might intend to place in the city. Experience has shown that it may take quite some time to obtain such permissions, and the letter would show that this has already been taken care of, and thus increase the feasibility of the application.
BR, /Jan-Olov, OrganiCity team