You can use an iPad or iPhone or an Android device.
The number of devices is not limited.
First, you need to have an account to use this feature.
Then you can log in with the same email address to another device.
To use the app on another device
download the app from App Store or Play Store
log in with the same email address you used to Sign up
Compatibility between platforms
Given the difference between Apple and Android software kits, the apps and account are not compatible.
Invoice Maker Pro is not accessible through a website.
There is no app for Windows or Mac.