Yes,

You should add status codes maybe starting from 100 and assign for example 101 if the key doesn’t exist, 102 if the max number activation has been reached, 103 if the key is expired.

Now I have to do calculate on my side if the key is expired, would be great if your plugin can generate a status code for it.

Also, for don’t know the reason, when I var_dump on my testing website the generated json for error contains only the first item “code:”, while when testing on Postman it appears with all the items.
The success json has all the items on testing website and Postman.

That’s really weird

starting from 4xx is fine, the most important thing is that they have different numbers so I can assign different translated error messages from my side. At the moment the errors are identified from different messages in english from you plugin json.

2: this is the way I retrive the json, in case of success all the items are displayed, in case of error only the first item “code” is displayed:

// this is for Debug
$decoded 	  = $this->get_key_access();
var_dump($decoded);

public function get_key_access() {
		$url          = SWAL_WEBSITE_URL . "/wp-json/lmfwc/v2/licenses/$this->key?consumer_key=$this->ck&consumer_secret=$this->cs";
		$decoded_body = $this->get_decoded_body( $url );

		return $decoded_body;
	}

/**
     * 
	 * Utility function to get json body from URL request
	 * 
	 */
	public function get_decoded_body( $url ) {

			$response = wp_remote_get( $url );
			if ( 200 === (int) wp_remote_retrieve_response_code( $response ) ) {
				$body         = wp_remote_retrieve_body( $response );
				$decoded_body = json_decode( $body, true );
			}
		if ( ! empty( $decoded_body ) ) {
			return $decoded_body;
		}

		return false;
	}

I was assuming that data->status on error json had the same meaning of data->status on success json.

But yes, you can actually modify the code parameter to make unique for every error. That would be great.