A document must not include more than one “meta” element with a “http-equiv” attribute whose value is “content-type”.

A document can have only one meta element with http-equiv="content-type", so keep a single encoding declaration and delete the rest.

<meta http-equiv="content-type" content="text/html; charset=utf-8"> is the older way to declare a page's character encoding. HTML treats it as an encoding declaration, just like <meta charset="utf-8">, and a document may contain only one. The validator reports an error for every extra copy, even when all of them say utf-8. It also ignores case in the http-equiv value, so Content-Type and content-type count as the same declaration.

Duplicates usually come from templates. A base layout writes the declaration, then a partial or a plugin adds it again further down the head. Find every copy in the rendered page, keep the first one and delete the others.

You can also swap the one you keep for the shorter <meta charset="utf-8"> and put it first in the head, so it sits within the first 1024 bytes of the document. Don't keep both forms, though: the validator rejects a meta charset next to a meta http-equiv="content-type" with a different error.

Invalid example

<!DOCTYPE html>
<html lang="en">
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>Products</title>
  <meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body>
  <p>Hello</p>
</body>
</html>

Valid example

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Products</title>
</head>
<body>
  <p>Hello</p>
</body>
</html>

Learn more:

MDN Reference

HTML meta element - MDN

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MDN Reference

meta http-equiv attribute - MDN

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