A quick update.
There is a field in the provided software where you can switch the protocol from Growatt to Victron (and about 6 other brands), but this field only appears when the password is entered.
I changed the protocol to Victron, and now i’m getting the right message IDs in candump;
can0 TX B E 305 [8] 00 00 00 00 00 00 00 00 '........'
can0 TX B E 307 [8] 12 34 56 78 56 49 43 00 '.4VxVIC.'
can0 RX - - 356 [8] D3 14 0A 00 04 01 00 00 '........'
can0 RX - - 35A [8] A9 AA AA 02 A9 AA AA AA '........'
can0 RX - - 35C [8] C0 00 00 00 00 00 00 00 '........'
can0 RX - - 35E [8] 52 6F 61 72 50 6F 77 65 'RoarPowe'
can0 RX - - 35F [8] 4C 69 0A 0A 00 00 00 00 'Li......'
can0 RX - - 370 [8] 52 6F 61 72 50 6F 77 65 'RoarPowe'
can0 RX - - 371 [8] 72 20 34 38 2F 31 30 30 'r 48/100'
can0 RX - - 372 [8] 01 00 01 00 00 00 0F 00 '........'
can0 RX - - 373 [8] 03 0D 05 0D 2A 01 2C 01 '....*.,.'
can0 RX - - 374 [8] 30 31 00 00 30 30 30 30 '01..0000'
can0 TX B E 305 [8] 00 00 00 00 00 00 00 00 '........'
can0 TX B E 307 [8] 12 34 56 78 56 49 43 00 '.4VxVIC.'
can0 RX - - 375 [8] 30 34 00 00 30 30 30 30 '04..0000'
can0 RX - - 376 [8] 30 31 00 00 30 30 30 30 '01..0000'
can0 RX - - 377 [8] 30 31 00 00 30 30 30 30 '01..0000'
can0 RX - - 378 [8] 00 00 00 00 00 00 00 00 '........'
can0 RX - - 379 [8] 10 27 00 00 FF 25 00 00 '.'...%..'
can0 RX - - 380 [8] 30 4A 48 50 42 59 38 45 '0JHPBY8E'
can0 RX - - 381 [8] 32 52 30 30 51 30 30 30 '2R00Q000'
Battery capacity is not yet correct, but i’ll take that up with the manufacturer and get a new firmware - its sending the capacity as mAh, but the GX is interpreting it as Ah, and the number of online/offline is wrong, but these are minor;
I now have another working system!
Thanks everyone!