AX 2012 R2 introduced a few changes to how we associate a Dynamics Online payment service to your AX company. The Sign up now and Link account options we saw in AX 2012 RTM have been removed from the payment service window. In order to set this up in Accounts receivable >> Setup >> Payment >> Payment services, you would need to manually link the accounts. The steps below will walk you through connecting a payment service that is readily active in Dynamics Online to your AX company.
1. Go to www.dynamicsonline.com
2. Select For Customers.
3. Log in with a Microsoft Account (also known as Windows Live ID).
NOTE: If this auto logs you in with an account that is saved in the browser, go to Live.com and sign out first.
4. Select Service List in the left navigation pane.
5. Find the payment service that you would like to link to your AX company.
6. Copy the Service ID from ID field.
7. Leave this window open and switch to AX.
8. Go to: Accounts receivable >> Setup >> Payment >> Payment services
9. In the Service account ID field, paste the copied ID from Dynamics Online.
10. Enter in the Microsoft account and Microsoft account password.
NOTE: This is also known as your Windows Live ID. The user entered here must also be set up with access to that payment service in Dynamics Online partner or customer portal.
For steps on setting up user roles, click the following link: http://blogs.msdn.com/b/axsupport/archive/2013/03/06/dynamics-online-user-roles.aspx
11. The Environment field is already populated as PROD and this should be left as is.
12. Highlight and copy the entire Public key. As a test, paste the contents into a text document to ensure it copied the contents properly. This is a fairly large key and at times this has a tendency to copy the fields in the form instead of the key. If this happens, simply close the payment services window and reopen it to try the copy again.
13. Switch back to the Dynamics Online customer portal.
14. Click User management in the navigation pane.
15. Click New System User
16. Paste in the Public Key into the Public Key field.
17. (Optional) Change First and Last name. I recommend doing this to know which company this system user is for if you have more than one payment service set up.
18. Click Save.
19. Select the System User we just created by placing a checkmark next to it.
20. Click Edit.
21. Add the specific system user roles for that payment service or all roles to the Selected Roles by clicking on the >> sign.
22. Click Save.
23. Switch back to the AX payment services window.
24. Click Credit Card Types menu button.
25. Ensure these are properly configured. 
26. Click Close.
27. Click Validate.
This should validate successfully and you can now process credit cards.
If you do receive an error during validation, the two most common issues are:
- the user account or system user account is not set up with proper access Dynamics Online
- firewall settings are blocking the service, check to ensure https://paymentservice.dynamics.com/dlpaymentservice.asmx can pass through