Please help to fix these Site Errors!

Hi Team,

While running the site audit in SEMrush(a SEO tool), I got few errors in my website.
1. incorrect page found in sitemap.xml – This is on my checkout page:
Site map URL: https://niladrika.com/page-sitemap.xml
page url: https://niladrika.com/checkout

2. structured data item is invalid – This is on my FAQ page.
page URL: https://niladrika.com/faqs/
Error Desc: Field Issue Description (mainEntity- A value for the mainEntity field is required.)

Please help me to resolve these issues.

Regards