https://mercuryo.io/ (half way down the page)
https://www.checkout.com/docs
https://transak.com/

Examples of the 'competition'
1) https://www.moonpay.com/
2) https://global.transak.com/?utm_campaign=Website%20Conversions&utm_source=homePage&utm_medium=menu&utm_term=buy-crypto
3) https://kriptomat.io/best-fiat-to-crypto-on-ramp/