You cannot hold local fiat currency in your account; you can however use your local currency to add money into your your account.

In other words, if you're in Nigeria, you cannot hold Nigerian Naira directly in your account. You can however use Nigerian Naira to add funds to your account; those funds will automatically be in the form of digital currency, such as USDc. This enables you to have full custody of your funds, and may help de-risk currency fluctuation, too.
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To learn how to deposit into your account using local fiat payment methods, see here.