thanks, thank you

In general, use thanks not thank you. It's OK to use thank you in content that has a formal tone or is about a serious subject, such as cybersecurity or privacy.

Don't use thanks unnecessarily. Use thanks as the closing in email, a letter, or a similar message. Otherwise, thank the customer only when they've been inconvenienced or they went out of their way to do something.

Examples
Thanks for your feedback.
Microsoft offers a 10 percent military discount as a way to say thank you for your service.