XF 1.5 Paid Upgrades not auto updating

[squirrly]

I'm getting these errors in the server error log:

Stack Trace
Zend_Http_Exception: Invalid HTTP response version: 2 - library/Zend/Http/Response.php:182 Generated By: Unknown Account, 46 minutes ago
#0 /home/thebaby/public_html/forum/library/Zend/Http/Response.php(665): Zend_Http_Response->__construct(200, Array, '\x1F\x8B\x08\x00\x00\x00\x00\x00\x00\x03\ns\r\xF2t...', '2', false) #1 /home/thebaby/public_html/forum/library/Zend/Http/Client.php(1007): Zend_Http_Response::fromString('HTTP/2 200 \r\nse...') #2 /home/thebaby/public_html/forum/library/XenForo/UserUpgradeProcessor/PayPal.php(180): Zend_Http_Client->request('POST') #3 /home/thebaby/public_html/forum/payment_callback.php(24): XenForo_UserUpgradeProcessor_PayPal->validateRequest(false) #4 {main}

So, PP is notifying my forum that the purchase happened, but xenforo isn't processing it successfully. Any ideas why?

 

[squirrly]

Any chance anyone could help here? We're preparing for an upgrade to 2.1, but I'd like to get this fixed in 1.5 if at all possible.