I have had further contact from resell.biz, It turns out that the problem is due to the domain I am trying to transfer is currently hosted by another resell.biz re-seller.
"It is possible to move domain names between customer accounts at Resell.biz, however, the "move services" option must be used instead of the transfer. Also, unlike a transfer the "move" must be initiated at the current location. In other words, domain "moves" are pushed, whereas domain transfers are pulled."
So in other words it appears that the other re-seller has to first move the domain over to me, and then clients can renew their registration with me.
This concerns me though, as if anyone tries to transfer their domain over to me and their current host is a resell.biz re-seller whmcs will throw up this error in my console, and accept payment, then the client will get frustrated as to why extra steps are required. Has anyone else had experience with this, or does anyone have any ideas how this could be automated? Do other domain registars have the same process?
Am i best to dump resell.biz and switch to someone else? do either Enom or reseller club have the same process?