Cash App Card, Venmo, Zelle, PayPal and Apple Cash cards are not accepted on the debit card method, the Debit tile on the Deposit screen.
That method takes debit cards issued directly by a bank, and the card provider declines prepaid and virtual cards, Apple Cash included, whether you use them directly or through Apple Pay.
Revolut cards are declined on the debit card method for the same reason, so retrying the same card does not help.
Some accounts see Cash App listed under Exchanges and apps on the Deposit screen.
If yours does, you can deposit that way: choose it, complete the payment in Cash App, and the funds arrive as USDC in your fomo wallet once the payment goes through.
The options under Exchanges and apps differ by account, location and device, so not everyone sees the same ones, and the tile is in the mobile app. The steps are in https://help.fomo.family/en/articles/17909459-depositing-with-cash-app.
If you have a bank issued debit card, you can use it in the mobile app through Debit on the Deposit screen: the Deposit cash screen offers Apple Pay or Google Pay where it is available to your account, or your debit card under Details.
Alternatively you can deposit USDC directly from another wallet or exchange. In the app, go to Deposit, then Crypto, select the same network as the USDC you are sending from, and copy the deposit address.
Only send USDC on the same network the address is for. On Robinhood Chain the deposit asset is USDG, and the screen shows the minimum for the network you selected.
Sending Bitcoin from Cash App is not a fomo deposit path. Bitcoin is not a supported network, so a Bitcoin send never reaches your fomo wallet.