About This HTML Issue
A field with the readonly attribute can't also have aria-readonly="false": remove aria-readonly and let the native attribute set the state.
The readonly attribute on an <input> or <textarea> already tells browsers and assistive technologies that the user can't change the value. aria-readonly="false" claims the opposite, so the field exposes two conflicting states. The ARIA in HTML specification forbids aria-readonly="false" on any element that has readonly, and the validator reports it as an error.
This often comes from a component or template that always outputs aria-readonly from a flag that defaults to false, while readonly is added separately. Decide what the field should be. If users shouldn't edit it, keep readonly and drop aria-readonly. If they should, remove readonly. aria-readonly is meant for custom widgets, such as an element with role="textbox" or a grid cell, which have no native readonly attribute.
Writing aria-readonly="true" next to readonly doesn't trigger this error. That combination is only redundant, and the validator reports it as a warning.
Invalid example
<label for="account">Account ID</label>
<input type="text" id="account" name="account" value="AC-1042" readonly aria-readonly="false">
Valid example
<label for="account">Account ID</label>
<input type="text" id="account" name="account" value="AC-1042" readonly>
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