Issue
PayPal returned API error code 81002 - Method Specified is not Supported.

Cause
PayPal identified your provided method as "unspecified" because it detected coding errors.

Solution
Debug your code. Replace or correct any invalid or deprecated variables.

Possible solutions:

• Do not use urlencode + http_build_query, because this will result in double encoding.
• Check that you aren't using a semicolon (;) as a separator. PayPal supports use of only ampersands (&) as separators. 
• Review your code to ensure that none of the variables in it have been deprecated.

For help resolving this issue or others, visit PayPal's Contact Customer Service page.
 

Note: See the Developer Portal for a complete list of NVP/SOAP API error codes.

See also:
NVP/SOAP Reference