Resolve issues in a PHP script or in a VPS windows server 2022

hi, I recently purchased this php script from https://codecanyon.net/item/swipgle-easy-file-transfer-saas/31169348 and installed it on my VPS server in my domain www.wesend.pt. Initially i needed help from the developers to install the solution as it didn't run smoothly. For two days everything seemed to work correctly, the files were transferred and the emails sent, until it started giving error 500. When talking to the developers they claim that the problem is in my VPS, as I don't have enough technical knowledge, I need a technician who is able to assess the situation and get the script working correctly. You can see the error in attachment or just test it in my website.