Using React fetch gives pyramid.exceptions.PredicateMismatch: The resource could not be found - reactjs

Question

I am writing a React web client that use a REST API to communicate to a Python Pyramid backend. Problem is that only the methods POST and GET works. All other give error on the server. Also I can only use the "Accept' header, all other give the same error:
pyramid.exceptions.PredicateMismatch: The resource could not be found.
It works fine from Android app, using CURL, using Postman, and REST API plugins in browser mode. But for the fetch command in React it do not work.
Server Side:
config.add_route('admin_language_api', '/api/admin/language')
def allow_CORS(config, log):
def add_cors_headers_response_callback(event):
def cors_headers(_, response):
response.headers.update({
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Methods': 'POST,GET,DELETE,PUT,OPTIONS',
'Access-Control-Allow-Headers': 'Origin, Content-Type, Accept, Authorization',
'Access-Control-Allow-Credentials': 'true',
'Access-Control-Max-Age': '1728000'
})
event.request.add_response_callback(cors_headers)
config.add_subscriber(add_cors_headers_response_callback, NewRequest)
#view_config(route_name='admin_language_api',
request_method='DELETE',
renderer='json')
# #auth.require_api_auth
def delete_language(request):
React side:
export async function PServLanguagePost(languageObj) {
const data = await fetch('http://localhost:6543/api/admin/language', {
method: 'DELETE',
body: JSON.stringify(languageObj)
});
return await data.json();
}
Server ERROR:
2021-05-07 04:53:34,041 INFO [pyramid_debugtoolbar:287][waitress-3] Squashed pyramid.exceptions.PredicateMismatch at http://localhost:6543/api/admin/language
traceback url: http://localhost:6543/_debug_toolbar/31383138393039313238303136/exception
Pyramid dump:
request:
<Request at 0x228d20ffca0 OPTIONS http://localhost:6543/api/admin/language>
attr:
{'environ': {'REMOTE_ADDR': '127.0.0.1', 'REMOTE_HOST': '127.0.0.1', 'REMOTE_PORT': '56013', 'REQUEST_METHOD': 'OPTIONS', 'SERVER_PORT': '6543', 'SERVER_NAME': 'waitress.invalid', 'SERVER_SOFTWARE': 'waitress', 'SERVER_PROTOCOL': 'HTTP/1.1', 'SCRIPT_NAME': '', 'PATH_INFO': '/api/admin/language', 'QUERY_STRING': '', 'wsgi.url_scheme': 'http', 'wsgi.version': (1, 0), 'wsgi.errors': <_io.TextIOWrapper name='<stderr>' mode='w' encoding='utf-8'>, 'wsgi.multithread': True, 'wsgi.multiprocess': False, 'wsgi.run_once': False, 'wsgi.input': <_io.BytesIO object at 0x00000228D35C7040>, 'wsgi.file_wrapper': <class 'waitress.buffers.ReadOnlyFileBasedBuffer'>, 'wsgi.input_terminated': True, 'HTTP_HOST': 'localhost:6543', 'HTTP_USER_AGENT': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0', 'HTTP_ACCEPT': '*/*', 'HTTP_ACCEPT_LANGUAGE': 'en-US,en;q=0.5', 'HTTP_ACCEPT_ENCODING': 'gzip, deflate', 'HTTP_ACCESS_CONTROL_REQUEST_METHOD': 'DELETE', 'HTTP_REFERER': 'http://localhost:3000/', 'HTTP_ORIGIN': 'http://localhost:3000', 'HTTP_CONNECTION': 'keep-alive', 'waitress.client_disconnected': <bound method HTTPChannel.check_client_disconnected of <waitress.channel.HTTPChannel connected 127.0.0.1:56013 at 0x228d33c93d0>>, 'webob._parsed_cookies': ({}, ''), 'CONTENT_LENGTH': '0', 'webob.is_body_seekable': True, 'webob._parsed_query_vars': (GET([]), ''), 'webob._cache_control': ('', <CacheControl ''>)}, 'registry': pyramid.registry.Registry({}), 'invoke_subrequest': <bound method Router.invoke_subrequest of <pyramid.router.Router object at 0x00000228D1D07610>>, 'pdtb_id': '32333734333436323130343634', 'finished_callbacks': collections.deque([]), '_headers': <webob.headers.EnvironHeaders object at 0x00000228D33C9B80>, 'pdtb_sqla_queries': [], 'request_iface': <InterfaceClass pyramid.request.admin_language_api_IRequest>, 'response_callbacks': collections.deque([]), 'matchdict': {}, 'matched_route': <pyramid.urldispatch.Route object at 0x00000228D358EA00>, 'root': <pyramid.traversal.DefaultRootFactory object at 0x00000228D33C9C10>, 'view_name': '', 'subpath': (), 'traversed': (), 'virtual_root': <pyramid.traversal.DefaultRootFactory object at 0x00000228D33C9C10>, 'virtual_root_path': (), 'locale_name': 'en', 'exception': <PredicateMismatch at 0x228d35d8160 404 Not Found>, 'exc_info': (<class 'pyramid.exceptions.PredicateMismatch'>, <PredicateMismatch at 0x228d35d8160 404 Not Found>, <traceback object at 0x00000228D3448C40>)}