When attempting to park a call, the error "call transaction failed" is received, and it is necessary to attempt the operation multiple times before succeeding. The behavior does not seem to be consistent across attempts and the issue is not straightforward to reproduce.
This issue has been found to occur in relation to the use of SIP ALG, which is not supported in Kandy. As a workaround, it is recommended that alternative ports in which Kandy is listening (other than the default 5600) are used instead:
The parameter to change this value depends on the specific device. In the case of Yealink, 'account.1.sip_server_port' should be used.