Navigate to your Shopify store admin panel. 

In the Account Status section, Click "Manage"

In a new tab,  Navigate to https://admin.portone.cloud/

Navigate to the previous tab, and paste the "PortOne Key" in the field as shown below. Now click on "Verify Now"

After clicking on "Verify Now", on successful configuration, you'll be redirected to the PortOne Payments settings page, to verify the configuration click on "Manage"

As you can see the verification is now completed.

PortOne Key
This is the public key on the PortOne admin dashboard.
You've verified this installation on PortOne
Verify Again

This completes the configuration of PortOne on Shopify.

How to set up PortOne on Shopify