To retrieve a topic URL from the appropriate webservice, you need to know the following information:
user : Pseudo of a forum administrator
pwd : Password of a forum administrator
idforum : ID of the forum where the topic is located
idcat : ID of the category where the topic is located
idtopic : ID of the topic which URL we want to retrieve
idpost : You can ask for the URL of a specific reply in the topic. Leave this empty if you only want the topic URL.
A PHP example:
The webservice will return 2 parameters
siteurl : the URL of the Website
pageurl : the URL of the topic