Bamboo build variables are not getting substituted in plan Webhook Notifications url

Summary

When we try to configure a notification based on commit id hash as the url end point , using "bamboo.planRepository.<position>.revision" variable the variable value is not getting substituted in the url.

Infact None of the build variables are getting substituted in the notifications url.

Steps to Reproduce

Try to integrate Bamboo with GITHUB.
Try sending Bamboo build status to GITHUB end point url.

It is not able to recognise the plan variable "bamboo.planRepository.revision" or "bamboo.planRepository.1.revision" and giving an error. When i give the complete url as below it works fine.

Works fine :- https://api.github.com/repos/anikredngold/testingcommit/statuses/dd61b5f6509dab2d109abaf2c5fd8f1b42151e41

Has issues:- https://api.github.com/repos/anikredngold/testingcommit/statuses/${bamboo.planRepository.revision}