I cannot match transactions with invoices via the app. qbo error..... the website is not mobile phone user friendly

Let me help you sort out this error, Simon. 

QuickBooks Online (QBO) matches up transactions and even suggests it as payment for the invoice. But before we start, may I know what specific error are you getting? If you're unable to match transactions, these are the possible scenarios that prevent  the program from matching:

• Verify that the transaction has not been reconciled.
• Verify the transaction was entered using the same bank account.
• Make sure the Quickbooks Online transaction has not been previously matched to another bank-downloaded transaction.
• If it is a deposit or payment received, make sure it is not on the Bank Deposit page (undeposited).

But, if you're still having issues when matching, let's refresh your data to see the latest available information in your QBO application. Here's how:

For iOS

1. Go to Settings, then tap General.
2. Tap iPhone Storage, then tap the QuickBooks Online app.
3. Tap Offload App.
   This will free up the storage without deleting your app's documents and data.

For Android

1. Go to Menu ☰, then tap More Options ⋮.
2. Tap Settings, then Refresh Data.
3. Tap YES to confirm.

However, I still recommend matching your transactions using a web browser. To learn more on how to quickly scan matched transactions and approve them using the QuickBooks Online app, check out this article for more information: Match Your Bank Transactions In The QuickBooks Online App.

Moreover, learn how you can identify any differences between the balances of the two accounts. I've added this article for more details: Reconcile An Account In QuickBooks Online.

If you have any questions along the way, I'd be happy to lend a hand.