Concatenate string in the template

Question

I have to prepare a url on the fly in the template by passing some variables to it.

{% with init_sync_url='/baseurl/formid/'|add:form_id|add:'/context/' %}
     =={{init_sync_url}}===
       {% myother_tag goto_url=init_sync_url  %}
{% endwith %}

This code works pretty fine. Which also shows me the output on the template:

==/baseurl/formid/abcd123/context/===

Which is OK. But after that when I add the a context variable cntxt containing a string like - '01-01-1030'

{% with init_sync_url='/baseurl/formid/'|add:form_id|add:'/context/'|add:cntxt %}
       {% myother_tag goto_url=init_sync_url  %}
{% endwith %}

OR

 {% with init_sync_url='/baseurl/formid/'|add:form_id|add:'/context/' %}
           {% myother_tag goto_url=init_sync_url|add:cntxt  %}
 {% endwith %}

This throws an error!!! Don't know, why? I expect the output if I log the line in the template inside with tag
=={{init_sync_url}}===:

==/baseurl/formid/abcd123/context/01-01-1030===

- Is the hyphen("-") causing something?

(Detailed error in pastebin)

NOTE - Just In case if any django developer knows the answer to my question. There is not much difference in the filters of django & Chicagoboss.