People often use the words to mean the same thing, but they’re different.
If an exterminator puts signs and banners in front of a fancy house when they’re inside killing rats, that’s promotion. But it’s not good marketing.
Marketing is creating the conditions for a story to spread so you can help people get to where they hope to go. Marketing is work that matters for people who care, a chance to create products and services that lead to change.
Promotion can support that. Or it might simply be a selfish hustle for attention.
If you have to interrupt, trick or coerce people to get the word out, you might be doing too much promotion and not enough marketing.