While I’d love to help with this issue, there seems to be missing information. You mentioned the error you notice in the tag assistant and the code you’ve installed on your website but did not provide the specific details about the error or the code. However, I can outline the common problems one might face.
Generally, this problem could be due to a variety of reasons. Maybe the GA4 tag is possibly not installed correctly on your site. Ensure that the tag is present on every page of your website, it’s in the right spot (between the tags), and not altered in any way.
There could be a problem with the conversion tracking setup on Google Ads. Make sure the conversions you want to track are properly defined and linked to your Google Ads account, and the conversion ID is entered correctly.
Also, keep in mind the conversions won’t register instantly, there might be a delay. Plus, be sure that your Ads are receiving enough traffic. If your ads are not getting sufficient clicks, then there might not be enough data for conversions to show up.
Finally, it could be that users are blocking Google Analytics or ad tracking, or that your site has issues with cookies.
If you can provide the specifics of your situation, it would be easier to provide a more accurate solution.
If nothing helps, it’s recommended to hire a professional who specializes in Google Ads conversions to troubleshoot the issue in detail.