I have extensibly working with Magento APIs lately. At one instance I got error “invalid API path”. After some digging around, I found the solutions and issue that caused it.
This issue is caused when the magento API call is not defined in the XML definition of the API file. The original API call was “catalog_product.create” and I used “product_catalog.create” so this was the reason for “invalid API Path” error in Magento API.
Hope this information helps.