You can not create sub totals with native FileMaker portal records. For that you need use some other techniques like Virtual Lists, ExecuteSQL and show portal in List view.
A. The portal on Total Sales Tab is just going to Invoice, not Invoice Row. Therefore it is only showing first record. Make the portal go to Invoice Detail instead and you will see all details for each invoice
B. In other tabs on Customer you can not go to Invoice Detail and then back up to Invoice. You need to add another Table Occurrence after Invoice Detail to Invoice to be able to see correct date
C. Seems like you have a Filter on the Portal that you can delete straight away.
I noticed that for both portals the problem are correlated, if i change the portal total sales tab to go thru invoice row it will display incorrect dates but if i only go thru invoice only will only display 1st record on each invoice.
Would you kindly illustrate how to make that table occurrence that you said and how it works, btw, just got computer with filemaker installed and we are planning to switch from pc to apple so im trying to migrate the access db to filemaker. Still exploring filemaker and was hoping can get faster answers in forums where people deal with it on daiy basis.