It's actually telling you what the problem is...
2018051703 is Moodle 3.5.3.
You either need to upgrade your Moodle (good idea!) or find the correct version of the theme for Moodle 3.5.1
It's actually telling you what the problem is...
2018051703 is Moodle 3.5.3.
You either need to upgrade your Moodle (good idea!) or find the correct version of the theme for Moodle 3.5.1