When I viewed any RSS (XML) page on my WordPress site, the page didn’t render correctly and instead displayed an error stating: XML declaration allowed only at the start of the document.

Upon viewing the page source I could see that the first line in the document was in fact blank line, and the second line contained the usual XML declaration:

<?xml version="1.0" encoding="UTF-8"?>

But what was causing it?

It turned out that the problem was with my custom theme.  In Functions.php in my child theme folder, I had whitespace before the starting <?php and after the ending ?>.  Once I deleted this whitespace and re-uploaded Functions.php to my web server, the blank first line was gone and all of my RSS pages rendered successfully!  Hopefully this will enable you to solve the error message: XML declaration allowed only at the start of the document.

 

XML declaration allowed only at the start of the document
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