I just found this other forum post, which might be the answer to my issues: https://forum.mysensors.org/topic/5671/loosing-my-mind-sensor-not-talking-to-esp-gw-latest-2-2-0-beta/2

I too have bought the radios with a blob instead of an IC.

I too have ordered different radios - the ones that are recommended here in the shop.
Had just hoped to be able to figure out how to get the ones I have to work. If anyone have any other ideas, or would like me to post some code, please let me know. I am running pretty standard from the example, only added MY_NODE_ID in the top...

@mfalkvidd Should both the gateway and the sensor have static id's? (different of course)

It seems to me that the sensor is trying to find a parent, but fails?

@David Well, I just saw an update to the boards had been released, so first I tried updating that, but resulting in the same error.
Then I downgraded the boards to version 1.6.11 as recommended in the thread you linked to, but still resulting in the same error.

But thanks for the tip... Well, am really scratching my head on this problem.

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Can anyone verify that a controller is not needed for the communication between the sensor and the gateway to work?
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I have now rewired all the cables, and made it neat, plus changed the radio, but nothing helps...
I still get a:

!TSM:FFPAR:FAIL
!TSM:FAILURE

Now I downgraded to version 2.0, but the same problem remains.
It seems that the problem resides with the sensor?
At least it is the sensor that complains...
Or is my problem that I am trying to run this without a controller?

TSM:PDT
TSM:INIT
TSM:RADIO:OK
TSP:ASSIGNID:OK (ID=254)
TSM:FPAR
TSP:MSG:SEND 254-254-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSM:FPAR
TSP:MSG:SEND 254-254-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSM:FPAR
TSP:MSG:SEND 254-254-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
TSM:FPAR
TSP:MSG:SEND 254-254-255-255 s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=bc:
!TSM:FPAR:FAIL
!TSM:FAILURE

@mfalkvidd Kind of... Here is the log of the gateway in full length

0;255;3;0;9;MCO:BGN:INIT GW,CP=RNNGA--,VER=2.1.0
0;255;3;0;9;TSM:INIT
0;255;3;0;9;TSF:WUR:MS=0
0;255;3;0;9;TSM:INIT:TSP OK
0;255;3;0;9;TSM:INIT:GW MODE
0;255;3;0;9;TSM:READY:ID=0,PAR=0,DIS=0
0;255;3;0;9;MCO:REG:NOT NEEDED
0;255;3;0;14;Gateway startup complete.
0;255;0;0;18;2.1.0
0;255;3;0;9;MCO:BGN:STP
0;255;3;0;9;MCO:BGN:INIT OK,TSP=1

If this helps... I will try using the older version of the sketch for both the sensor and the gateway...

Tried with a ceramic 47 micro farad condenser to no avail...

I have hooked up the Arduino Pro mini with the sensor to a laboratory power supply, which should be very precise. No change in the log...

0 MCO:BGN:INIT NODE,CP=RNNNA--,VER=2.1.0
4 TSM:INIT
4 TSF:WUR:MS=0
12 TSM:INIT:TSP OK
14 TSF:SID:OK,ID=3
16 TSM:FPAR
114 TSF:MSG:SEND,3-3-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
2123 !TSM:FPAR:NO REPLY
2125 TSM:FPAR
2226 TSF:MSG:SEND,3-3-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
4235 !TSM:FPAR:NO REPLY
4237 TSM:FPAR
4337 TSF:MSG:SEND,3-3-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
6346 !TSM:FPAR:NO REPLY
6348 TSM:FPAR
6449 TSF:MSG:SEND,3-3-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
8458 !TSM:FPAR:FAIL
8460 TSM:FAIL:CNT=1
8462 TSM:FAIL:PDT
18466 TSM:FAIL:RE-INIT

Will try with a larger capacitor, even though I don't think it will do much difference, when I use this power supply...

@Fabien I am not using a controller. Can it run alone, or can I set up the Arduino Mega gateway as a controller as well?