422 SMTP error Microsoft 365 Relay

Hi, we have different WP sites on a single VPS. Some use PostSMTP and some use FluentSMTP. All FluentSMTP sites started showing this error today (emails were sent just fine until yesterday). PostSMTP sites don’t show this error.

{
  "code": 422,
  "message": "SMTP Error: Could not connect to SMTP host. Connection failed. stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages: error:0A000086:SSL routines::certificate verify failed",
  "errors": null
}