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-# SuperFaktura API client
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+# SuperFaktura API client
+
+Library for handling of SuperFaktura API.
+
+Environment variables:
+- `SUPERFAKTURA_API_KEY`: can be found in your SuperFaktura account (*Tools > API access*).
+- `SUPERFAKTURA_API_URL`: url depends on the [Base URLs](README.md#base-urls)
+- `SUPERFAKTURA_API_EMAIL`: can be found in your SuperFaktura account (*Tools > API access*).
+- `SUPERFAKTURA_API_COMPANY_ID`: can be found in your SuperFaktura account (*Tools > API access*).
+
+## Base URLs
+
+Base URLs for different SuperFaktura versions.
+
+| Country        | URL                             |
+| -------------- | ------------------------------- |
+| Slovakia       | https://moja.superfaktura.sk    |
+| Czech republic | https://moje.superfaktura.cz    |
+| Austria        | https://meine.superfaktura.at   |
+| Sandbox (SK)   | https://sandbox.superfaktura.sk |
+| Sandbox (CZ)   | https://sandbox.superfaktura.cz |