LedgerSMB comes with a web service API . The version number assigned follows the rules of semantic versioning.
The current major version is 0 (zero), meaning that it’s not considered to have stabilized yet. The main reason is that not all functions have been ironed out yet: filtering, sorting and pagination are to be specified and implemented.
The API is hosted on erp/api/v0, on the same root as login.pl.
That is to say that if LedgerSMB’s login screen is hosted at
https://example.org/login.pl
then the API can be found at
https://example.org/erp/api/v0.
The definitive API definition is in the source code located at doc/openapi/API.yaml.
There is also a web reference version at
https://docs.ledgersmb.org/openapi/1.13.0/LedgerSMB-api.html
Note that the above URL is LedgerSMB version dependent. There may be newer versions available and you should refer to the version that matches your installation.