Standard practice is to use the Xero bank reconciliation process. More information on this can be found on the Xero link below, but in general terms the bank statement is imported into Xero and then you reconcile the payments to the invoices. This way it is based on money actually received opposed to the remittance advice which may not be correct. If the trading partner is paying multiple invoices in one payment then the remittance advice (820) can be normally used to view the invoices to apply the payment to.
The 820 is not a required document, and is unique to each trading partner/customer as to if and how you would like to trade it. If you would like to trade the 820 with one of your Trading Partners today, you are able to utilize the SPS Fulfillment platform to do so. If you have questions on how to use Fulfillment for the 820,SPS can organize additional information/training on this.