No option to enable Apple Pay on Watch
Please check the region your iPhone and your Apple Watch are set to. This is a quote from Apple.com, emphasis mine:


  
  Make sure that you're in a supported region.
  
  
  For your iPhone or iPad, go to Settings > General > Language &amp; Region, then scroll to Region.
  For your Apple Watch, open the Watch app on your iPhone, go to the My Watch tab, tap General > Language &amp; Region, and check the region
  format.
  
  


I had a similar issue in the past and was able to solve it after setting the correct region and restarting both devices.

Let me know if it worked for you as well.