I have enable vendors to be able to access the backend admin page however, when I used a vendor account and clicked the product designer option, it just takes me to the homepage. What should I do?

It seems you are using a marketplace plugin... maybe Dokan!
When a vendor registers on you website he will no be admin! He will be Vendor (or other role you define)
To access backend not all roles are allowed and, maybe Vendor are not allowed to access backend. You must change permissions in order to allow other roles to access backend and use fancyproduct designer.
Hope it helps

I am using dokan and I have followed this guide.

https://support.fancyproductdesigner.com/support/solutions/articles/13000059724--dokan-let-vendors-sell-customizable-products-with-fancy-product-designer

 If I turned off admin access, the page just says they are not allowed into that link. This this case, I have allowed vendors to access fancy product designer but when clicking product designer it just takes me to the homepage

Maybe something related with your theme that you can fix with custom CSS. Maybe the link created bettween theme and plugin is incorrect and you can fix with CSS

im currently using storefront theme and the only plugins i have are woocommerce, dokan and FPD. Do you have pics showing where i can fix it?

Also, the product designer button in the vendor dashboard is linked to this url http://sitename.com/wp-admin/admin.php?page=fancy_product_designer

Do you mind just for testing porpuse to swith your theme to twe twe 2 and check if the problem persists?

Yes I did tried that using 2024 and 2022 but the issue still persist

If you as admin are able to click FPD link and it works and as Vendor it redirects you to homepage and it happens with all themes, im pretty sure its related to roles. i would advise you to install user role editor and check what Vendor arent able to do (FPD and admin panel related) that Admins are!

I do have Members – Membership & User Role Editor Plugin and I am not sure which permission to grant without risking the site. Can you perhaps provide some options that i should be looking at? Thank you for your time! 

I have found the issue it is because of woocommerce HPOS. Thank you 

I have found the issue it is because of woocommerce HPOS. Thank you