# Appendix

- [Demo](/appendix/demo.md)
- [Widget Signature Demo](/appendix/demo/widget-signature-demo.md)
- [API Signature Demo](/appendix/demo/api-signature-demo.md)
- [Webhook Validation Demo](/appendix/demo/webhook-validation-demo.md)
- [Languages](/appendix/languages.md)
- [Fiat Currencies](/appendix/fiat-currencies.md)
- [Cryptocurrencies (on-ramp)](/appendix/cryptocurrencies-on-ramp.md)
- [Cryptocurrencies (NFT Checkout)](/appendix/cryptocurrencies-nft-checkout.md)
- [Errors](/appendix/errors.md): Error codes & messages