Decrypting user-api-key payload after login

I have been trying to obtain the User-Api-Key for a third party login by decrypting the payload, after making the call to user-api-key/new on the iOS platform.
The problem with that is the base64 decode goes fine, but the decryption throws an error (code -50) when I implement decryption with SecKeyCreateDecryptedData as well as SecKeyDecrypt classes. For info code -50 is sign - input buffer bad size which implies the cipher text is longer than the key which makes RSA obsolete.

I tried matching the encrypted strings on my local discourse instance and the iOS platform, though most characters remain the same, on converting the encrypted string to Data, the size becomes larger than the keySize. I suspect that has something to do with decoding the base64 payload string to obtain the encrypted text. Am i wrong? Or am i missing something?