Hello Bharat,
First as you define a category in your headContributions i would add this category to your headContribution so <@hst.headContribution keyHint=“demo” category=“htmlHead”>.
And second it was mentioned in a recent post [1] that headContribution accepts a single element. So wrap each meta tag you want to contribute in <@hst.headContribution tags
Hope this helps and kind regards.
Lef
[1] https://community.bloomreach.com/t/multiple-elements-inside-headcontribution-throwing-error/528