I haven't found a place with information about this issue. I started a queue using power dialer and every call results in "ININ-OUTBOUND-BUSY" in the outbound side. I can see the API results and all of the json responses have the pattern:
See Wrap-up codes assigned by outbound dialing for information about that wrap code. ININ-OUTBOUND-BUSY means that the call received a busy signal and was terminated. If you need assistance determining why that particular number is giving you a busy signal, you can try opening a case with Genesys Cloud Care, but it's more likely that you'll need to contact your telephony provider to assist with troubleshooting. (If you're using PCV, that's Care)