This code sets the payment name to the value of the Text form field

additional-parameters-for-stripe-gateway.php

<?php

add_action(
    'jet-form-builder/gateways/before-create',
    function ( $request ) {
        if (
            // execute this action only when paying through Stripe
            ! is_a(
                $request,
                \Jet_FB_Stripe_Gateway\Compatibility\Jet_Form_Builder\Actions\Create_Checkout_Session::class
            ) ||
            // You must have JetFormBuilder >= 3.1
            ! function_exists( 'jet_fb_context' )
        ) {
            return;
        }

        // where 'text_field_name' - form field name
        $value = jet_fb_context()->get_value( 'text_field_name' );

        $request->set_payment_name( \Jet_Form_Builder\Classes\Tools::to_string( $value ) );
    }
);

Thank you Laxus!