Even though your church is not a business, in California it was probably organized as a "Religious Corporation" under the California nonprofit corporations law. Corporations in California, even churches, are required to file a "Statement of Information" with the California Secretary of State's office. You are required to file the first one within 90 days of being incorporated, and then every year afterwards. The part of the law in California that requires a corporation to file a statement of information is California Corporations Code Section 1502. That is probably the section 1502 that is mentioned in the letter you received.
Your church can file the form, or you can hire somebody to file it for you. Without seeing the letter that you received, it's not clear who the letter is from. There are some companies that will send you a letter that looks official, telling you that you need to file the statement of information, and they will offer to do it for you for a fee. That might be the type of letter you received. Or, you might have received a letter from the Secretary of State's office telling you that your form is overdue and that you owe a late fee. However, the current late fee for a nonprofit corporation is $50, so it is very unlikely that the letter you received asking for $243 came from the Secretary of State.
You can also go to the California Secretary of State's website and search for your church in the database of corporations (https://bizfileonline.sos.ca.gov/search/business). It will tell you when the next Statement of Information is due and whether it is late.
You can also contact an attorney who works with nonprofit corporations and show them a copy of the letter you have received. They can tell you what you should do next.