Gravity Forms restrict file upload file size for specific form.php

Replace the **formid** and **fieldid**

/*** Gravity Forms - Restrict the file upload size for Guest Blog form
–––––––––––––––––––––––––––––––––––––––––––––––––– ***/
add_filter( 'gform_validation', 'validate_file_size_form_name' );

function validate_file_size_form_name( $validation_result ) {
    $form = $validation_result['form'];

    // Specify your target form ID
    $target_form_id = **formid**;

    // Check if the current form is the one you want to target
    if ( $form['id'] != $target_form_id ) {
        return $validation_result;
    }

    foreach ( $form['fields'] as &$field ) {
        // Check if the field is a File Upload field and has the specific field ID
        if ( $field->type != 'fileupload' || $field->id != **fieldid** ) {
            continue;
        }

        // Construct the field ID for $_FILES
        $field_id = 'input_' . $field->id;
        if ( isset( $_FILES[ $field_id ] ) && !empty( $_FILES[ $field_id ]['name'] ) ) {
            $file_size = $_FILES[ $field_id ]['size'];

            // Set your size limit (300KB in this case)
            if ( $file_size > 300 * 1024 ) {
                $validation_result['is_valid'] = false;
                $field->failed_validation = true;
                $field->validation_message = 'File size must be less than 300KB.';
            }
        }
    }

    $validation_result['form'] = $form;
    return $validation_result;
}