The too many attempts or too many requests message means several deposit attempts were made in a short window, and the payment system has temporarily paused further tries. It is a rate limit from the payment processor, not something fomo controls.
Wait at least one hour before trying again. Depending on how many attempts were made, the cooldown can last longer. Closing and reopening the app will not reset the timer.
Trying again before the cooldown ends can reset the timer and extend the wait further.
While you wait, check that you are using a bank-issued debit card and that your billing address matches exactly what your bank has on file. Those are the two most common reasons a deposit fails before the lockout kicks in.
If you would rather not wait, you can add funds by depositing USDC. Go to Deposit, then Crypto, select the network your USDC is on, copy the deposit address, and send only USDC on that same network.