Credits not showing on invoice email that was paid by it

[bear]

Client has a small overpayment. It was added as a transaction and the next invoice was paid using it. 
The invoice is marked as paid, but the line says this in the email: Credit Applied: $0.00 USD. The ledger on the invoice shows it was applied, but strangely:
Type: Client Account Debit, with "Applied Credit Note funded by Client Credit" for the description.

As far as the client  could see, it was paid, but no idea how. My clients don't typically log in and review, but just look for the email. 
This used to work back in the day, quite simply. Now it's confusing for admins, and worse, clients. Can it be made to show this (latest version WHMCS)? Not seeing any merge fields that might do it.

[Damo]

There is no way we have found. Occasionally customers double pay the same invoice. 

In v8 it would put the account in credit, then the credit balance would get used and shown on the invoice (not as the transaction at the bottom). 
 

v9 has changed this behaviour. And transactions are applied different ways and shown differently in the emails and PDFs  

Have you tried viewing the client account statement? 

[bear]

Fun. 
 

Quote

Error: Call to a member function lte() on false in /home/xxxx/public_html/clients/modules/reports/client_statement.php:194
Stack trace:
#0 /home/xxxx/public_html/clients/xxxx/reports.php(0): unknown()
#1 {main}

Looks like it may be just the one client has the error, but don't see how this will help resolve the confusion.

Edited 3 hours ago by bear

[Damo]

Sadly it doesn't resolve the confusion. It does contribute to showing that it's broken.

I had to look at the transactions list to be able to make some sense of these changes. Customising the email templates is something I did to reduce confusion.

[bear]

Likely have to do the same with the templates. Something akin to "if your invoice is marked as paid while you hadn't yet submitted a new payment...."
Was WHMCS made aware of this, do you know?

A search reveals the error may be caused by malformed dates in either transactions or invoices. Searching this client, they have two old invoices (long before v9) that were canceled when they decided to drop a few domains. The canceled ones have date paid as "0000-00-00" (along with timestamp of zeros), which might be causing it. No way to fix it, since invoices are immutable within WHMCS now, even to the point of deleting canceled ones. Also can't add a date in that paid field, since that would indicate it's paid....
What a mess.