You have to escape + sign with \
Try:
ADDR="$ETN_ADDRESS\+$ETN_WORKER"
Didn´t work because it puts the "\" into the address like this
etnadress\+workername
and that fails because the pool is not expecting to see the "\" in there. It only expects to see the "+" expression in between the etnaddress and the workername.
Sorry, my bad. No need to escape + in this case. Any of these 4 examples should work:
ADDR=$ETN_ADDRESS+$ETN_WORKER
ADDR="$ETN_ADDRESS+$ETN_WORKER"
ADDR=$((ETN_ADDRESS))+$((ETN_WORKER))
eval ADDR="$ETN_ADDRESS+$ETN_WORKER"