Vadim, I can't log into the admin panel:
https://prnt.sc/u514ddPlease clarify a few points.
What exactly did you find when processing the oneboxsync.php file
https://prnt.sc/u51ge4?Have you registered access for the database user from the onebox ip address?
Has the database host changed since the migration? And if so, did you change it in the integration settings?
In general, please check the correctness of the settings following this algorithm:
https://prnt.sc/mqxi8n and give feedback. Thank you.