Joomla 6.1.2 + solidres4.1.0 - unsupported opperand types: string / int during

Environment
- Joomla 6.1.2
- Solidres 4.1.0 Stable
- PHP 8.5.9
- MariaDB 10.11
- HTTP 500
-json: ubsupported operand types
testsite / administrator now also returns 500 ( possible separate issue)

Issue
The booking form works normally until the Guest Information step. When clicking Process (Bank Wire or Pay Later), the request fails.

Network request:
index.php?option=com_solidres&task=reservation.process&step=guestinfo&format=json

Server response:
{"error":true,"code":0,"message":"Unsupported operand types: string / int"}

HTTP status: 500

Already checked
- Property is set as Default.
- All 14 Solidres extensions are version 4.1.0.
- Bank Wire and Pay Later plugins are enabled.
- Rates and occupancy settings appear correct.
- The issue occurs consistently on a fresh test booking.

Hi,

You should enable the Joomla Debug Mode and set Error Reporting to Maximum, then try again to see the full error trace.