Weird CORS problem with POST requests - getting desperate now!

Hi, my application has an Angular 5 front end and a Laravel 5.5 backend. I can't get POST (or PUT) requests to work. I've installed the Spatie laravel-cors package. GET requests work fine. The POST requests work fine from Postman, but not from Chrome or Firefox. The error I get in the Chrome console is:

Failed to load http://MYDOMAIN.co.uk/public/api/module/: 
Redirect from 'http://MYDOMAIN.co.uk/public/api/module/' to 'http://MYDOMAIN.co.uk/public/api/module' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:4200' is therefore not allowed access.

In Firefox the error is:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://MYDOMAIN.co.uk/public/api/module/. (Reason: CORS header 'Access-Control-Allow-Origin' missing).

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://MYDOMAIN.co.uk/public/api/module/. (Reason: CORS request did not succeed).

It appears to be trying to '301 redirect' POST requests (although it doesn't seem to specify where to)- but it doesn't seem to do it with Postman,

The Headers list as shown by Chrome is:

General: 
Request URL: http://MYDOMAIN.co.uk/public/api/module/ 
Request Method: POST 
Status Code: 301 Moved Permanently 
Remote Address: xxx.xxx.xxx.xxx:80 
Referrer Policy: no-referrer-when-downgrade

Response Headers: 
Connection: Keep-Alive 
Content-Length: 246 
Content-Type: text/html; charset=iso-8859-1 
Date: Wed, 01 Aug 2018 13:37:51 GMT 
Keep-Alive: timeout=5, max=100 
Location: http://MYDOMAIN.co.uk/public/api/module 
Server: Apache

Request Headers: 
Provisional headers are shown 
Accept: application/json, text/plain, / 
Content-Type: application/x-www-form-urlencoded 
Origin: http://localhost:4200 
Referer: http://localhost:4200/managemodules 
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36

htaccess in the main laravel root folder is:

Options +FollowSymLinks RewriteEngine On

RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_FILENAME} !-f RewriteRule ^ index.php [L]
php -- BEGIN cPanel-generated handler, do not edit
Set the “ea-php70” package as the default “PHP” programming language.

AddType application/x-httpd-ea-php70 .php .php7 .phtml
php -- END cPanel-generated handler, do not edit

htaccess in the public folder is:

Options -MultiViews -Indexes

RewriteEngine On

\# Handle Authorization Header
RewriteCond %{HTTP:Authorization} .
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

\# Redirect Trailing Slashes If Not A Folder...
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} (.+)/$
RewriteRule ^ %1 [L,R=301]

\# Handle Front Controller...
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [L]

In kernel.php I have the Spatie package:

protected $routeMiddleware = [
    'auth' => \Illuminate\Auth\Middleware\Authenticate::class,
    'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
    'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,
    'can' => \Illuminate\Auth\Middleware\Authorize::class,
    'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
    'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
    'jwt.auth' => 'Tymon\JWTAuth\Middleware\GetUserFromToken',
    'jwt.refresh' => 'Tymon\JWTAuth\Middleware\RefreshToken',
    'cors' => '\Spatie\Cors\Cors::class',
];

In the api.php file I have the route defined:

Route::post('module', 'ModuleController@create')->middleware('cors');
Route::get('modules', 'ModuleController@listmodules')->middleware('cors'); 
Route::put('module', 'ModuleController@update')->middleware('cors'); 
Route::delete('module/{moduleid}', 'ModuleController@delete')->middleware('cors');

I'm really pulling my hair out. I've been trying to get this working for days. Can anyone suggest anything? It will be something obvious but I'm so close to it I can't see the wood for the trees.

Thanks

Andy