Forget CardNet or VisaNet for online processing here, they are a pain.
Their API's are hard to work with and they are really not set up to do online processing. Plus their rates are ridiculous.
The only half decent option in the DR is done by a Colombian company.
Soluciones de Recaudo Electronico, pagos en línea en Colombia y Republica Dominicana | eCollect, Recaudos, PSE Colombia, Visa, Mastercard, Amex, Credencial, Diners, VisaNet, CardNet |
If your serious about processing, then you need to do it out of the USA.
The rates are much better and they understand what "online" means.