Public Key Acquired instead of Access Token

[solitarychild]

Retrieving access token using a third party API returns:

{
".tag": "requires_captcha",
"public_key": <Public Key>
}

instead of 

{
".tag": "success",
"user_id": <user id>,
"oauth2_access_token": <access token>
}

What could be the cause?

[Greg-DB]

Please open an API ticket with details, sample code, etc. so we can look into it:

https://www.dropbox.com/developers/contact

Thanks!