Instance ID: 82ce7cb0-3324-49a3-b968-170da40da417 Error Code: #0
Instance ID: 82ce7cb0-3324-49a3-b968-170da40da417 Error Code: #0
Probably the vendor folder is incomplete / some file got corrupted.
I'd redownload the FOSSBilling release you're running and then replace the installed vendor folder with the one in the newly downloaded zip file.