Cake Wallet supports four providers for selling cryptocurrency for fiat: DFX.swiss, Onramper, MoonPay, and Kryptonim. Which of them you actually see depends on your region and on the asset you are selling.
Tap Buy on the balance card to open the Buy/Sell page, then switch to Sell to see the providers available to you.
DFX is only available for European customers.
Cake Wallet shows an Onramper widget that aggregates many providers. If you have an issue with the widget itself, please contact Cake Wallet support. For an issue with the provider behind your order, find the support details for that provider on the Onramper help site.
MoonPay supports selling Bitcoin, Bitcoin Cash, Litecoin, USD Coin, and Tether.

