CSRF with fetch API

I tried adding it (to the code I posted earlier), but it broke everything. This is what I got in the logs:
#0 C:\laragon\www\stostolov\vendor\codeigniter4\framework\system\Security\Security.php(233): CodeIgniter\Security\Exceptions\SecurityException::forDisallowedAction()
#1 C:\laragon\www\stostolov\vendor\codeigniter4\framework\system\Filters\CSRF.php(85): CodeIgniter\Security\Security->CSRFVerify(Object(CodeIgniter\HTTP\IncomingRequest))
#2 C:\laragon\www\stostolov\vendor\codeigniter4\framework\system\Filters\Filters.php(173): CodeIgniter\Filters\CSRF->before(Object(CodeIgniter\HTTP\IncomingRequest), NULL)
#3 C:\laragon\www\stostolov\vendor\codeigniter4\framework\system\CodeIgniter.php(378): CodeIgniter\Filters\Filters->run('front/fetchProd...', 'before')
#4 C:\laragon\www\stostolov\vendor\codeigniter4\framework\system\CodeIgniter.php(308): CodeIgniter\CodeIgniter->handleRequest(NULL, Object(Config\Cache), false)
#5 C:\laragon\www\stostolov\public\index.php(45): CodeIgniter\CodeIgniter->run()

Also I tried to simply include the csrf value in the body (see below) - but it didn't work either.
fetch(SITE_CONSTANT+'/whatever', {
method: "post",
body: csrf_val
}).then(response => console.log(response))

You can see things I made with codeigniter here: itart.pro its not overly impressive as I have very little time to learn.