(WordPress SEO by Yoast) post_tag-sitemap.xml not working in sitemap. Plz help

Hello.

I’m having problem with my sitemap_index.xml when I open any ” post_tag-sitemap.xml ” it says Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 128 bytes) in /home/naqash/public_html/wateentv.com/wp-includes/cache.php on line 569
my sitemap is https://wateentv.com/sitemap_index.xml if I open any tag sitemap it gives above error you can see this. https://wateentv.com/post_tag-sitemap3.xml

Plzzz Help me to solve this problem
thank you.

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