It is important to point out that having a positive balance (also known as funds, wallet, etc) is necessary to be able to send messages. Here you can check how the SMS service is charged.
In summary, even if you are using the free plan, every sent message incurs a cost.
You can top up your account by following these steps:
1. Click on Billing settings
2. Select the amount
3. Fill your billing information.
4. Select Bank Transfer
And click the button Pay with Wire transfer:
5. Finalize the payment
The payment details will be shown, including the IBAN and Reference.
6. Contact us via chat or email to send us the payment receipt.
Afterward, your corresponding balance will be enabled, and an invoice will be generated for you to download.
You might be interested in learning how to top your account using PayPal
You might be interested in learning how to top up your account by Credit card