@raven_corwin 
To validate a field that depends on another field in Symfony, you can make use of Symfony's validation constraints and create a custom validation constraint. Here is an example of how you can do this:
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// src/Validator/Constraints/DependentFieldConstraint.php
namespace AppValidatorConstraints;
use SymfonyComponentValidatorConstraint;
/**
 * @Annotation
 */
class DependentFieldConstraint extends Constraint
{
    public $message = 'The value of field "%dependedField%" is required when field "%field%" is "%condition%"';
    public $field;
    public $dependedField;
    public $condition;
}
 | 
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// src/Validator/Constraints/DependentFieldValidator.php
namespace AppValidatorConstraints;
use SymfonyComponentValidatorConstraint;
use SymfonyComponentValidatorConstraintValidator;
class DependentFieldValidator extends ConstraintValidator
{
    public function validate($value, Constraint $constraint)
    {
        // Get the value of the depended field
        $dependedFieldValue = $this->context->getRoot()->get($constraint->dependedField)->getData();
        // Do the validation based on the condition
        if ($constraint->condition === 'some_condition' && !$dependedFieldValue) {
            // Validation failed, add a violation
            $this->context->buildViolation($constraint->message)
                ->setParameter('%field%', $constraint->field)
                ->setParameter('%dependedField%', $constraint->dependedField)
                ->setParameter('%condition%', $constraint->condition)
                ->addViolation();
        }
    }
}
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# config/validation.yaml
AppValidatorConstraintsDependentField:
    - AppValidatorConstraintsDependentFieldValidator
 | 
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use AppValidatorConstraintsDependentField;
// ...
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('field')
        ->add('dependedField', null, [
            'constraints' => [
                new DependentField([
                    'field' => 'field',
                    'dependedField' => 'dependedField',
                    'condition' => 'some_condition',
                ]),
            ],
        ]);
}
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In this example, the dependedField will be validated based on the provided condition. If the condition fails, a validation error will be displayed with the message defined in the DependentFieldConstraint class.
Remember to customize the conditions and validation rules as per your requirements.