Solution for 401 Unauthorized in App Store Connect API: Convert DER-encoded Signature to 64-byte Format If you keep encountering a 401 Unauthorized error when making requests to the App Store Connect API, even though your JWT seems valid, the issue likely stems from how the signature is encoded. The App Store Connect API requires the signature in a 64-byte binary format, but many libraries output the signature in DER encoding by default. This difference causes the API to reject the JWT, leading to the 401 error. To fix this, you need to ensure that the signature is converted from DER encoding into the required 64-byte binary format before sending the request. This often involves using specific methods or libraries to handle the conversion. By ensuring the correct format for the signature, your JWT will be valid, and the API should accept the request without the 401 error. Hope this helps!