The key to getting buy-in from stakeholders is to build a business case that supports your idea. When you build a business case, it shows to your stakeholders that you're solving a problem that they're having.

Asana: The beginner's guide to writing an effective business case

If there is resistance to your idea then you need to understand why. Change the approach from “us against them” to “help me understand why” so you will definitely understand their point of view. When you reframe it to, "Hey, I see this is very problematic for you, I want to understand why, help me understand." They will take the time to tell you.

Start a conversation with the people who are pushing back and ask “what would change your mind?” Try to understand why they feel the way they do. Do not make assumptions. You get buy in by sitting with the stakeholder and understanding what the issue is.

Don't be afraid of the conversation! Go into difficult conversations with a mindful attitude and that you are there to understand.

Read "Nonviolent Communication" because it helps you express your needs and let others express their needs in order to get into this conversation in the best possible way. Marshall Rosenberg: Nonviolent Communication: Create Your Life, Your Relationships, and Your World in Harmony with Your Values

It can also be a matter of not having the right timing with the project.

You are a part of the bigger people team. It’s all about attracting, retaining and developing talent and those translate into very clear KPIs.

Ask yourself what is the contribution of the people team to the company. You can gather the data with simple tools and then think what you can do with those. Also take into account measuring the initiatives that you do on a regular basis like onboarding process and leadership program. You want to see the before and after and the changes there.