If your 8.1 gateways are older than the signing jar, you need to either upgrade the gateways (so that a signed jar is distributed) or adjust the 8.3 designer launcher to allow unsigned jars (worse for security). See advice in this thread:
If your 8.1 gateways are older than the signing jar, you need to either upgrade the gateways (so that a signed jar is distributed) or adjust the 8.3 designer launcher to allow unsigned jars (worse for security). See advice in this thread: