After you have saved your shop's domain (i.e. shop-domain.com) in the Custom Domain field of your Shop Settings.
For those who are using GoDaddy, after logging in, proceed to Domains Management and select your shop's domain.
Then in the Zone Edit tab, proceed to the CName section to enter your Marketplace Shop URL (e.g. kimstore.tackashop.com) in the Points To column.
If you enter www in the Host column, then your shop will load as www.shop-domain.com .
If you enter * in the Host column, then anything can be assumed. (e.g. shop-domain.com, anything.shop-domain.com)
For those who are using Web.com.ph, after logging in, select your shop's domain.
Then in the right column, proceed to Add DNS Records to enter your Marketplace Shop URL (e.g. pimpkicks.tackashop.com) in the Rdata field.
Enter www in the Host field, and select IN CNAME as the Type.
If you need both www.shop-domain.com and shop-domain.com to point to your shop, add another A record to your DNS by selecting Type IN A.
Then, enter 18.104.22.168 (for Philippines) or 22.214.171.124 (for Singapore) in the Rdata field, leaving the Domain field empty.