PDI mPay PDI mPay allows you to pay for gas or in-store purchases through your mobile phone at participating PDI/ZipLine merchants. Ensuring secure transactions to your bank account or credit card account, the app transmits location data for you to pay at the pump. Just sign in with your email and select your pump number to begin your transaction. When your transaction is complete, you can review transaction information within the app and in an email. PDI mPay is free to download.