Measurement protocol, ofline conversion and sGtm

Currently we send purchase (order) events to GA via measurement protocol.
As the purchases happening offline few days after the order, we would like to send Purchase events to GA, GAds an FB, few days after the order, when we have more info about it.
I found the hint how to do it with GoogleAds:.

What is the recommended way to do it with GA. One way is to send it directly, but is it the right way, if I want to work with the data stape Store?