Custom post type and custom taxonomy archive inaccessible

Finally I found the solution.
I think the problem was because I didn’t specify the rewrite rules for taxonomy archive page manually because I thought that I just want some simple url (default) so I didn’t have to add the rewrite rule at all.

So I tried the following code and add some flush rules hooked during activation of the theme:

add_rewrite_rule('tax-1/([^/]+)/\?posttype1=([0-9]+)?$', 'index.php?tax-1=$matches[1]&posttype1=$matches[2]', 'top');

The Monkeyman Rewrite Analyzer stating the following was also very helpful that I thought of that way:

This query variable is not public and will not be saved

It thus brought me to this link: How to properly rewrite url by custom var