prohibitedIf()

prohibitedIf($field, $value) rejects a non-empty value when the other field strictly equals the given value.

$rules->string('nickname')
    ->optional()
    ->prohibitedIf('accountType', 'business');

The comparison is strict. When the condition matches, a non-null and non-empty value returns a prohibited error before type-specific validation runs.

$registration = new Registration();
$registration->accountType = 'personal';
$registration->companyName = 'Acme';

$error = Rule::for($registration)
    ->string('companyName')
    ->optional()
    ->prohibitedIf('accountType', 'personal')
    ->validate();

The field may be empty in the prohibited context. Use requiredIf() when the desired behavior is to require a value instead.