Hi there,
We are developing a new site and we would like some help to find an api which provides a response to see if a certain location falls within the ULEZ and/or the Congestion Zone. An example if seen in the link below and screenshot from Tfl site.
Hello and welcome to the forum! 
Unfortunately, I don’t think we provide a public API to check whether a given location falls within those zones.
We do, however, provide JSON and Shape files for the zones as open data:
Please be aware that the ULEZ will be expanding across all London boroughs from 29 August 2023:
