Sequence of connecting boxes?

[#1]

When the fibre service was installed at my house, the (Plusnet) engineer
said that the two white boxes had to be turned on in a set sequence.
I cannot recall which he said first, whether the BT box and then the
PlusNet box or vice versa!
Which is the order and more to the point why does the connection have to be
switched on in this order?

[#2]

The BT box should be turned on first, this establishes the connection to your local FTTC cabinet and synchronises the FTTC connection.
The Plusnet box is turned on next after the BT boxes led’s switch on to show the connection is up and stable, this box is the router and establishes the connection to the Plusnet servers and subsequently through them to the internet.
However the Plusnet box will wait until the BT box is connected even if you do switch them on in the opposite order.
Regards, P.

[#3]

It may or may not be helpful but one way to think about it is to turn the devices in order of shortest distance from the BT wall plate. So by that I mean whatever is connected to the wall plate turn that on first then what ever is connected to the device connected to the wall plate that gets turned on next. For myself the order is:
Modems
Router
Switch
WiFi AP
PCs, Tablets etc.
But from what Pendragon says it may well not matter.

[#4]

I've just checked your connection chuffchuff and glad to see all is OK.
Shout up if you have any issues or questions!