Final Value Fees would account for the difference.

eBay's fee on your sale is 13.4%

eBay's fee structure is no secret.  If you were expecting to list and sell for free then you didn't read up on selling.

Some might come here and sympathise with you, saying something like "I understand your surprise, eBay blah blah blah", while others will point out that the 'missing' amount that you will never get is eBay's 'final value fee (including shipping)'

eBay does charge this fee on the transaction total (that includes postage), so $89.71 would indicate that you had a $14.50 (approx) postage charge.

13.4% of $669.50 is $89.71

Simples 🤔

On your numbers it's actually $79.71. As to when you can expect it - never. eBay is not a charity, as most sellers know. eBay even tell you that.

Hi there,   They are called Fees,(13.4% + 30c per sale), time to pay the ferryman.  You might also want a maths tutor or a new calculator.

Your 2  sales + postage actually  total   $665.00

$665.00  @ 13.4%  =  $89.11   + 

2  @  30c      =  60c

TOTAL    $89.71     (exactly what you were charged)

Go into Payments Tab, click on Payments,

then click on Payout ID No. that shows for that item (approx 10 digit no.) 

Then go into "View".

Clearly shows the fees plus breakdown of the final payment to you.