In order to accept payments through PosiPay you need to set it up with Stripe. PosiPay works exclusively with Stripe, and to get the most out of the integration you will want to set it up correctly. There are some steps to be completed in both your Salesforce org and in your Stripe Dashboard. If you don’t currently have a Stripe Account, you can find instructions on setting one up Create a New Stripe Account - PosiPay
Next place to go : Create a New Stripe Account - PosiPay