Allright, had to come back to say I got it working fine now!
Had to put it in the back of my garden (where it'll end up going anyhow) and got transmission going fine using some other code than the first example provided.
Opened the antenna casing to check the soldering and connections but all was fine there.
Still don't have a clue where the '62" code comes from but I now suspect it might have to do with needing to create a downlink callback on the SigFox backend.
Cool board anyhow. Am now transmitting info a couple of times per hour and it works really well.