errors in backend build with Node JS and connect with flutter apps

we have 2 mobile app as below :
customer app
specialist app
for diet center business
we have 3 issue on the apps as below :

chat module not working between customer app and specialist app (chat massages not working)
when specialist try to send the diet plan or working plan from specialist app to customer app its not sending
when customer try to change diet plan the price still show the same old plan (price not change)

after check from app developer they mention that all errors from backend and also the backend old developer was in Arabic

we have the source code of the two apps
and there is backend and database also live on digital ocean

app link in android :
customer :
https://play.google.com/store/apps/details?id=com.cambredge.cambredgeclient

specialist:
https://play.google.com/store/apps/details?id=com.cambredge.cambredgespecialist