I'm trying to create a customer and set the tag. This is what I'm doing:

$customer = $this->client->execute_kw($this->db, $this->uid, $this->pass,                       
 'res.partner', 'create',
 [                            
    [                                
        'is_company' => 1,
        'x_external_id' => $data['id'],                                
        'name' => $data['name'],                                
        'parent_id' => 1, //cf id                                
        'category_id' => [1], //tags                                
        'street' => $data['line1'],                                
        'city' => $data['town'],                                
        'state_id' => $this->_searchCounty($data['county_name']),                                
        'zip' => $data['postcode'],                                
        'website' => $data['website'],                                
        'phone' => $data['telephone'],                                
        'email' => $data['email'],                                
        'property_account_receivable' => 30,                                
        'property_account_payable' => 41,                                
        'customer' => true,                                
        'supplier' => true,                                
        'active' => true,                                
        'opt_out' => 1,                                
        'notify_email' => 'none'                            
    ]                        
]);

I would imagine passing an array with correct Id should have been enough, since this is how the tags show up when you read the record. But when the record is created, it doesn't have any tags attached to it, while all other passed information is present. Is there anything special about setting the tags via web services?