There can be many causes of pagination errors. One cause is a problem with the .htaccess file. Sometimes this can be corrected by going to the Dashboard, opening Settings->Permalinks, and clicking ‘Save Changes’.
Note that you do not have to actually change anything.
If this does not correct the problem, code changes may be required. Because you are using a purchased theme, we cannot examine its code or options. You should contact the theme supplier for help.