CoinpaymentsAPI

PHP Code:

use App\Libraries\coinpayments\src\CoinpaymentsAPI; 


This means that the class not only needs to be in this path, but also has a corresponding namespace.

It looks like you are using an official API wrapper.
You need to use loading via classmap.

PHP Code:

    public $classmap = [
        'CoinpaymentsAPI' => APPPATH . 'Libraries/coinpayments/src/CoinpaymentsAPI.php',
    ]; 


PHP Code:

use  CoinpaymentsAPI;
....
new CoinpaymentsAPI(...); 


Thanks for the answer that was the only thing I was missing the classmap