Permalinks Changing .org to .com

I’m developing a theme for a client and she purchased both the .org and the .com for her domain (www.morningstarzencenter.org), and the .com just redirects to the .org. When I try to make the permalinks fancy (actually, any of the permalinks do this), instead of changing for the .org, the links change to the .com and I get a 500 Internal Server Error.

For example, any of the permalinks for the blog posts will change what should be https://www.morningstarzencenter.org/post/ to https://www.morningstarzencenter.com/post/.

My menu bar doesn’t have this problem because I hard-coded the links into the php files.

Any thoughts on how to get this fixed?