What is the Form C-AR?

That's an important question. We'll quote the SEC directly (from here: 
https://www.sec.gov/info/smallbus/secg/rccomplianceguide-051316) to answer this question about the Form C-AR ("Form C Annual Report"):

e. Annual Reports
An issuer that sold securities in a Regulation Crowdfunding offering is required to provide an annual report on Form C-AR no later than 120 days after the end of its fiscal year. The report must be filed on EDGAR and posted on the issuer’s website. The annual report requires information similar to what is required in the offering statement, although neither an audit nor a review of the financial statements is required. Issuers must comply with the annual reporting requirement until one of the following occurs:

(1) the issuer is required to file reports under Exchange Act Sections 13(a) or 15(d);
(2) the issuer has filed at least one annual report and has fewer than 300 holders of record;
(3) the issuer has filed at least three annual reports and has total assets that do not exceed $10 million;
(4) the issuer or another party purchases or repurchases all of the securities issued pursuant to Regulation Crowdfunding, including any payment in full of debt securities or any complete redemption of redeemable securities; or
(5) the issuer liquidates or dissolves in accordance with state law.

Any issuer terminating its annual reporting obligations is required to file notice on Form C-TR reporting that it will no longer provide annual reports pursuant to the requirements of Regulation Crowdfunding.

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The Crowdfunding Professional Association (CfPA) recently held a webinar on complying with annual reporting requirements and you can find details here:  https://www.crowdfundingecosystem.com/events/nwnv2/cfpa-2023-webinar-series 

If you want to see the Form C (used to submit C-AR), here's a link to find it: https://www.sec.gov/files/formc.pdf 

@Scott McIntyre noted that an answer is also on the site of our hostess' company site: CrowdCheck  

https://www.crowdcheck.com/blog/form-c-ar-filing-time-again