Okay. This call is not possible without the JSAgent. I assumed that the customer is using a JSAgent since Hybrid applications consist mainly out of JS code. On the native side (Mobile Agent side) they can report a value. Documentation can be found here: https://www.dynatrace.com/support/doc/appmon/appmon-reference/glossary/visit-tag/
Sorry. The call is not possible was meant in the context of my other answer. Because dynaTrace.tagVisit() access the API of the JSAgent. So if you have got no JSAgent you can not use the API. But you can use manual instrumentation via the Mobile Agent and use one of the reportValues there. Afterwards you can use the documentation link to use a value that you reported as visit tag.
I am not sure if I understand you correctly. But in cases like this it is better to open a support ticket as we have to gather logs or see the environment to understand how the configuration looks like.