> For the complete documentation index, see [llms.txt](https://docs.ottpay.com/payment-api/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ottpay.com/payment-api/in-app-union-pay-secure-pay.md).

# API for Mobile with UnionPay-SecurePay

- [Payment Request API](https://docs.ottpay.com/payment-api/in-app-union-pay-secure-pay/payment-request-api.md)
- [Query Transaction API](https://docs.ottpay.com/payment-api/in-app-union-pay-secure-pay/query-transaction-api.md)
- [Code Samples(Web App, Android, iOS)](https://docs.ottpay.com/payment-api/in-app-union-pay-secure-pay/code-samples-web-app-android-ios.md): To invoke Union Pay-Secure Pay