The developer guide docs indicates that it is possible to use path-computation-request as an external REST API in order to invoke the PCE module for checking connectivity:

https://docs.opendaylight.org/projects/transportpce/en/latest/developer-guide.html#invoking-pce-module

However, this does not work in practice. The problem is that the servicehandler sets an input variable in the pce listener when receiving and processing a service request. If a path-computation-request is then sent through the external REST API, the pce listener will get a notification when path computation is finished and continue processing with the old input and new computed path. If the old input corresponds e.g. to a service creation, this will result in the service being re-created with the new path.

Since invoking the PCE module as described in the docs would be a useful feature, maybe this could be solved by resetting the input variable in pce listener after finishing processing a request.