There are a few reasons why Skype might ask for credit when you try to make a Skype-to-Skype call.

• Your Skype account may not have enough credit. Skype credit is used to pay for calls to landlines, mobile phones, and other countries. If you don't have enough credit, you'll need to purchase some before you can make a call.
• You may be calling a country that is not covered by your Skype subscription. Skype subscriptions typically cover calls to a limited number of countries. If you're calling a country that is not covered by your subscription, you'll need to purchase credit or upgrade your subscription.
• You may be calling a number that is not supported by Skype. There are some numbers that Skype cannot call, such as premium rate numbers and numbers that are blocked by the user's country. If you're trying to call a number that is not supported by Skype, you'll receive an error message.

If you're not sure why Skype is asking for credit, you can check your account balance and subscription status. You can also contact Skype support for help.

Here are some tips to avoid having to pay for Skype-to-Skype calls:

• Make sure you have enough credit in your account. You can check your account balance by signing in to your Skype account and going to the "Payments" section.
• Upgrade your Skype subscription. If you make a lot of Skype-to-Skype calls, you may want to consider upgrading your subscription. This will give you unlimited calls to a limited number of countries.
• Use a Skype credit card. You can purchase Skype credit cards at many retailers. This is a convenient way to add credit to your account without having to use a credit card online.
• Use a Skype calling plan. Skype offers calling plans that give you discounted rates on calls to landlines and mobile phones. This can be a good option if you make a lot of calls to countries that are not covered by your Skype subscription.