Working with mobile api - insertpm

[AlfaRomeoPortal]

Is there anybody that has been working with the mobile api?

Currently i am stuck at sending a pm reply.

I am doing a POST request to the api with the URL:

PHP Code:

http://www.alfa-romeo-portal.de/arcommunity/api.php?api_m=private_insertpm&api_v=7&api_c=2&api_api_sig=a535d4e8bad8484ce18d789d5ea10f02 


and the following post vars

PHP Code:

pmid=100953&message=test&title=blafoo&recipients=Andre 


The response always looks like this

PHP Code:

{"response":{"errormessage":["invalid_api_signature","Invalid API Signature"]}} 


Can anybody tell me what i am doing wrong?

THX