If you submit default robots.txt given by socialengine script in Google webmaster tool, the robots.txt tester shows error for sitemap: /index.php/sitemap?format=xml&rewrite=1
It shows- 'Invalid sitemap URL detected; syntax not understood'
Instead I wrote full url 'sitemap: https://domain.com/index.php/sitemap?format=xml&rewrite=1
And it worked.
Will it work for other search engines also ?
You would need to test and see. I am not sure what's up with Google.