See documentation at https://www.vismapay.com/docs/web_payments/
To install with composer, add following to composer.json and run ** composer update **
{
"require": {
"visma-pay/visma-pay": "^1.0.0"
}
}
For manual installation, you need to use provided loader
require './path-to-rest-php-lib/lib/visma_pay_loader.php';