Cannot modify header information - headers already sent by

I have an insert data php page that has been working fine for a year, hosted at GoDaddy Recently the ssl certificate updated and I had problems with only this website on my server. The website its self works fine, but I have an admin section for uploading data to MySql database. After the data is entered and submitted, the goto page is supposed to be: https://3dsound.org/protected/Event_Calendar_results.php I have the correct goto page listed in the php coding, but it goes back to a blank screen on this URL: https://3dsound.org/protected/Event_Calendar_insert.php If I highlight the url in the address bar and then hit my enter key the page insert page will come back up, Data is getting entered into the database OK.
I checked the error logs on the server and it shows this:

[16-Jan-2022 13:51:30 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/mississippi5/public_html/3dsound.org/protected/Event_Calendar_insert.php:1) in /home/mississippi5/public_html/3dsound.org/webassist/mysqli/queryobj.php on line 688

I don't know if it is a server problem or something on my site. I did upload a backup copy of the file and got the same results,
Thanks for your help

In some php versions you can't redirect if the page starts to write. In your case it looks like you may have a blank line or space on line 1 of Event_Calendar_insert.php. You can't have any blank lines or spaces above the <!doctype> tag.

Thank you very much Ray. That fixed my problem. I know PHP is very sensitive to code, but I missed that. Especially since the page had been working for some time.