Website not recieving PayPal payment data

Since the month of April numerous subscribers’ payments haven’t been registering on the site, even though they have been billed and their payment was successful with PayPal.

I am currently having to check PayPal routinely to find subscription payments, check the transaction number in PMS > Payments (not found), then manually add the payment for that user for them to be able to maintain access to the site.

License key is active and PayPal Express Checkout is selected.

I can’t seem to find any assistance when searching for this problem or a solution.

Thanks