Does not work with PayPal Standard

[andrewlimaza]

Describe the bug Seats aren't given when parent accounts purchase through PayPal Standard.

To Reproduce Steps to reproduce the behavior:

1. Set up your site to use PayPal Standard
2. For the parent account level settings, give a fixed number of seats and set it to include the price in the level price.
3. In incognito mode, purchase your parent level.
4. Upon returning from PayPal checkout and ensuring that the IPN has processed, see that there are no assigned codes or seats for the parent level.

Isolating the problem (mark completed items with an [x]):

• [x] I have deactivated other plugins and confirmed this bug occurs when only Paid Memberships Pro plugin is active.
• [x] This bug happens with a default WordPress theme active, or Memberlite.
• [x] I can reproduce this bug consistently using the steps above.

[MaximilianoRicoTabo]

It seems to me that this is not a Group Account bug but a core one. pmpro_after_checkout action hook is never triggered with Paypal Standard then the function callback that creates the Parent Group account never runs. Do we create a core bug instead ? @andrewlimaza