For festivals: NGOs have a special structure
Remember that you're not working with a professional organization or business, but rather with people working voluntarily on top of their regular jobs for a cause they consider very important. This means it might take them longer to answer or give you feedback. Also, sometimes your contact person might change while the project is already running. Please show some patience with people who have zero experience with festivals and who have no commercial interest.
Further, NGOs often have staff shortage. The COVID-19 pandemic has made the situation even more difficult. Therefore, they need more time for many processes (e.g., signing exhibitor contracts, creating social media material, staffing accreditations). You should take this into account in your overall planning and communicate it to the individual departments (marketing, accreditation, etc.).
NGOs often have volunteers with strong ideals. If your festival is co-financed by a sponsor with a dubious reputation, be prepared that some NGOs won't be willing to participate. Please respect this decision.
Holding an honorary position makes some volunteers expect preferential treatment at events. After all, they are working to change the world for the better, so some NGOs expect particularly intensive support "in return". You shouldn't underestimate this when mentoring NGOs. Taking care of social initiatives at a festival should be as important as taking care of your headliners and other artists. But also set limits and communicate when something is not feasible and why. Volunteers are fundamentally social people – they will understand.
Check out this video “Introduction to Nonprofit Organizational Structures” by NPCrowd to learn more about the different types of NGOs (English with English subtitles):