The deferred income GL posting could not be inserted

Turn debug to 2 in config.php and execute the transaction and post the results.

Which version of PHP and MySQL are you using? Looks like a PHP 8 issue where arguments for functions with default values are generally pushed to the end.

Try to do the same transaction in a fresh install of FA in PHP 5.x and MySQL 5.1 and you will note that NULL implementation and argument order may expose causes.

Lines 756-759 in reporting/includes/pdf_report.inc are:

    function TextCol($c, $n, $txt, $corr=0, $r=0, $border=0, $fill=0, $link=NULL, $stretch=1)
    {
        return $this->TextWrap($this->cols[$c], $this->row - $r, $this->cols[$n] - $this->cols[$c] + $corr, $txt, $this->aligns[$c], $border, $fill, $link, $stretch);
    }

The above function has not changed in 15 years.
However in 2 places in the said file certain PHP 8.1 issues caused a change 2 years ago for the likes of:

$str = ($str != NULL ? strtr($str, array("\r"=>'')) : "");

which may have to be revisited.

The function / method TextWrap is also defined in the same file (changed for PHP 8.1, 2 years ago) whilst the function / method addTextWrap called therefrom is defined in the file reporting/includes/class.pdf.inc.

Check if there are any PHP version related changes between PHP 5 and 8.1 that cause this situation.

@joe: any clues?

This doesn't make any sense to me.  There are no errors unless I do a report and I rarely need to do one. I don't even know what "The deferred income GL posting could not be inserted" means in the memo area of the deferred income account.  Does nobody know why that message would be inserted into the memo area of all prepayments.
I guess I'm also having trouble understanding how the prepayment and deferred income works.  When I look at the trial balances after the prepayments, I see the items in the deferred income, and also in the sales revenue account that the sales related to. But how does the deferred income know what year it is deferred to. I would have thought that it was the delivery date. And if so, why is it still sitting in the deferred income account. Do I need to move it around manually???

EDIT: OOPS!, so I do see that the prepayment did set the Delivery date correct (I marked it as delivered on the first day of the next fiscal). And the income account does show the items going into the revenue account on the date I set (first day of the next fiscal). So that all seems to be working (I think). I'm just not understanding why I would see that message in the memo field.  Could it be designed to do that and it is working properly??? I'm not a developer and so I can't really debug this on my own.

The code seems to be:

 if ($delivery->is_prepaid())
        {
                $deferred_act = get_company_pref('deferred_income_act');
                add_gl_trans(ST_CUSTDELIVERY, $delivery_no, $delivery->document_date, $deferred_act, 0, 0, 
                        "The deferred income GL posting could not be inserted",
                        -$total, null, PT_CUSTOMER, $delivery->customer_id);
        }

and to me that looks like this is just what gets entered into all prepaid items. So it's part of normal behaviour.
I would still like to know why it's worded like that. When one reads that it feels like it's an error.