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Since you are based in Rwanda, you can choose from any of these support payment gateways. Once you’ve created an account with one of these providers, you can connect that account in your Shopify admin following these steps:
From your Shopify admin, visit Settings > Payments.
Scroll down to the section Third-party providers and click Choose third-party provider.
Select your payment gateway.
Enter your account details.
Click Activate.
Please don’t hesitate to let me know if you run into any challenges!