@steen you've already had several threads around your problems getting zerotier to install on various low-flash devices. You have yet to confirm that a device with 8 MB of flash is sufficient or that 64 MB of memory is sufficient for it to run reliably. I'd strongly suggest you consider 16 MB of flash and 128 MB of RAM as a minimum.
For a couple dollars (or whatever your local currency is) more, a decent device in the same price range will save you time over the cheapest ones out there and likely be upgradable for much longer than one that is still RAM constrained, even if it has the marginal 8 MB of flash.
Your best resource for inexpensive devices continues to be
Now I found Nexx WT3020 locally but the Buyer say it is
Nexx WT3020F While on the bottom ticket writen Nexx WT3020 only without F
So How to ensure that is F ??
As it will different in Flash size ...
I love my Linksys WRT 32X, specially, cause I havent found any Problems untill now, with openWRT 18.1 on it, stable and RockSolid both together...and WLAN, WOW, I had some days ago a Brand New MacBook Pro here that is WLAN AC 1300 capaz, and I dled from my SSD HD, atatched to the Linksy WRT USB3 Port via WLAN 170/MB/sec !!! Faster then Gigabit Ethernet!! But, if the WRT32X is the best router arround...I cant say...as Im not able, to test them all myself