We are entering in reservations that were in the past and we want our payment date to match the date when we actually received it, not today.
We cannot change the payment date in group sales. It will always be the date you add the payment into Altru. Group Sales is considered a sales order in Altru, so the payment is always dated with the date you enter it, like sales orders in Daily Sales.
If this is functionality you would like to see added to Altru, please vote on this idea to subscribe.