About This HTML Issue
A field with the readonly attribute has an aria-readonly value that doesn't match it: remove aria-readonly and keep the native attribute.
aria-readonly only accepts true or false. A value such as TRUE, 1, undefined or readonly is neither, so the validator reports two errors on the same field: a Bad value error for aria-readonly, and this one, because the value differs from what readonly states. Values like these usually come from a template that prints a variable straight into the attribute, for example a boolean that the template language writes as 1 or True.
The readonly attribute already exposes the read-only state to assistive technologies, so the field doesn't need aria-readonly at all. Remove it. If you're building a custom widget that has no native readonly attribute, such as an element with role="textbox", write aria-readonly as exactly true or false.
Other values give different messages. aria-readonly="false" next to readonly is its own error, because it contradicts the native attribute. aria-readonly="true", or a value that exactly repeats the value of readonly (such as readonly="readonly" aria-readonly="readonly"), only gets a warning that the attribute is unnecessary.
Invalid example
<label for="account">Account ID</label>
<input type="text" id="account" name="account" value="AC-1042" readonly aria-readonly="1">
Valid example
<label for="account">Account ID</label>
<input type="text" id="account" name="account" value="AC-1042" readonly>
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