I could be wrong but I’m guessing that this challenge will be resolved if Mondo can id the transaction as a PayPal transaction and in which case, the transaction will be tagged / grouped automatically. The product team has a preference for avoiding manual user entry wherever possible.
There’s also a similar issue with Uber & Stripe transactions not being grouped correctly because additional characters are being added to the transaction labels.
In the meantime, my suggestion would be to tag these transactions. I’d recommend using emoji, rather than text to avoid typos & lower / upper character variations which will cause issues when you search for the ‘tag’, plus emoji are easier to spot when you’re scrolling through your transaction feed.
There’s a 
emoji for example…but worst case #PP might be an idea (hashtags being the most likely prefix for custom tags if Mondo ever supports them).
I use emoji to group my transactions for spend on taxis 
so I can get to the total for Uber + black cab combined & takeaways 
.
Once you’ve tagged your transactions, you can just search for the tag in the Home tab’s feed, apply any other filters you want & you’ll get the total amount spend + average transaction value at the bottom of the window 