Cannot Open PDF files in Teams tab

We have classic Teams App (not New Teams) with some tabs which are connected with SP folders from our SP site.  Teams users and SP users are the same (no access difference). We do not use Teams online only the App....

These SP folders has word, excel and pdf files.... 

when we open pdf files in the SP site - opens fine

when we open pdf files in Teams tab (which is connected with SP folder) it does not get open/view (below is the error screenshot). Note that we can open the pdf in browser only inside the Teams App we cannot view/open

would like to know any solution ?