The primary contact of the account has control over general settings which defines whether Buyers are able to pay with a credit card through B2B Payments.
Here's how you can control whether the 'Pay Now' button in the invoice is visible to (or hidden from) all Buyers.
General control in Payments Settings
From your main navigation bar, click on Payments > 'Settings'.
Under ENABLE PAYMENTS, you will see a toggle setting to 'Enable on Invoices' which is ON by default:

Only the primary contact can access and modify this setting.
You can disable B2B Payments for all Buyers by switching the toggle off and enabling only some Buyers to pay with a credit card or vice versa.
To enable (or disable) B2B Payments for certain Buyers, go into the Relationships section in QuickBooks Commerce to give access to individual relationships or relationships in bulk.
Team members who have user permissions set to 'Read & Write' for Relationships can make changes to enable (or disable) B2B Payments.
How to enable or disable B2B Payments access to Individual Relationships
Here's a quick tutorial:
From your main navigation bar, click on Relationships, select the individual relationship to enable (or disable) B2B Payments, and click 'Edit'.

Scroll down to see a B2B Payments drop-down.

Selecting the 'Enabled' or 'Disabled' will override the general settings and enable (or disable) the 'Pay Now' button for that particular Buyer.
If you choose 'Disabled', a payment using B2B Pay will not be allowed no matter the other values.
Enable or Disable B2B Payments access to Relationships in bulk
From the Relationships page, select the Relationships to enable (or disable) B2B Payments to in bulk by checking the box and selecting the appropriate bulk action.

Confirm that the selected Relationships are enabled (or disabled) to use B2B Payments and have access (or no access) to the 'Pay Invoice' button. Similarly, selecting 'Enabled' or 'Disabled' in bulk will override the general settings and enable (or disable) the “Pay Invoice” button for those Buyers.
B2B Payment Method Settings
Go to B2B eCommerce > Settings > Payments tab. If the Payment Method is set to 'None', payment is not allowed on the B2B store only.
Here are the common scenarios of B2B Payments and its relation to B2B:
- Enable on Invoices (Disabled), B2B Payments (B2B Payments), Relationship Settings (Default to General Settings) - means that payments will not be allowed on either the B2B store or Invoices sent to customers.
- Enable on Invoices (Enabled), B2B Payments (B2B Payments), Relationship Settings (Default to General Settings) - allows payments.
- Enable on Invoices (Disabled), B2B Payments (B2B Payments), Relationship Settings (Enabled) - allows payments.
B2B Payments does not accept/support the use of Discover Credit Card when paying for an invoice.