This is an attemps to integrate ZOHO invoice api in a php library. This library rely on guzzle and guzzle service description feature. It's very convenient to use that feature since it can validate your data from a json description schema (see guzzle doc). I'v began to compile Zoho invoice api parameters in services file you can find in "Services > ServiceFolder > ServiceFile.json"

This is a work in progress, feel free to fork and contribute if it can be helpful for you.