If you have problems getting buy-in from your stakeholders, try to involve them in what you’re doing. A senior stakeholder might want to have a voice. A developer might want her ideas to be taken into account. A financial advisor might want to have a say about the costs.
You don’t have to involve them fully in your project, but just enough so that they’ve been heard. And you might also get new and better ideas from cross-functional collaborators. Nobody wants to feel left out, and when they do feel that way, they object.
It’s well known that people will support you more when you engage them than when you just present to them. When you involve them, you’ll spend less time explaining, presenting, and convincing.