mga boss unsa problem ani nga code dili siya maka save error Error: INSERT INTO last thanks

<?php
include_once 'database.php';
?>
<?php






$query = "SELECT * FROM cruds ";
?>
<form method="post" action="process1.php">
<?php
$result1 = mysqli_query($conn, $query);
?>




<label for="inputEmail3" class="col-sm-9 col-form-label">Job Status:</label>
<select class="browser-default custom-select" name="jobstatus" class="form-control">
<option selected>Please Select</option>
<?php while($row = mysqli_fetch_array($result1)):;?>
<option value="<?php echo $row['user_id'];?>"><?php echo $row['user_id'];?></option>


<?php endwhile;?>




<br>



First name:<br>




<input type="text" name="first_name1">


<br>
Last name:<br>
<input type="text" name="last_name1">
<br>

<br><br>
<input type="submit" name="save" value="submit">
</form>


</select>



================================================


Error: INSERT INTO last (user_id,first_name1,last_name1) VALUES ('','ssssss','ssssss') Cannot add or update a child row: a foreign key constraint fails (`test`.`last`, CONSTRAINT `last_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `cruds` (`user_id`) ON DELETE CASCADE ON UPDATE CASCADE)