why am i getting Cannot add foreign key constraint error when migrating tables? - laravel-migrations

Question

Im trying to migrate my tags tables but i keep getting this error:
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table post_tag add constraint post_tag_post_id_foreign foreign key (post_id) references posts (id))
when running:
php artisan migrate:fresh
here is my code:
<?php
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreatePostTagTable extends Migration
{
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('post_tag', function (Blueprint $table) {
$table->bigIncrements('id');
$table->integer('post_id')->unsigned();
$table->integer('tag_id')->unsigned();
$table->foreign('post_id')->references('id')->on('posts');
$table->foreign('tag_id')->references('id')->on('tags');
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::dropIfExists('post_tag');
}
}
CreateTagsTable:
<?php
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreateTagsTable extends Migration
{
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('tags', function (Blueprint $table) {
$table->id();
$table->string('name');
$table->timestamps();
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::dropIfExists('tags');
}
}
How do i fix it?