[onlyoffice]When I was in configure onlyoffice tip: "Error while downloading the document file to be converted"

I have two nextCloud application servers, accessed using Apache, and configured with HTTPS.The front-end uses HAProxy for load configuration.
The OnlyOffice runs on another server that is the same network segment. And configure the HTTPS access, but in my noextcloud configuration onlyoffice tips I ā€œError while downloading the document file to be convertedā€

My nextCloud version is 19.0.1
The self-signed certificate used by the certificate
Does anyone have any good suggestions that can help me solve this problem?