Hi @Bikram Pal,
Thanks for your trust and we are pleased to offer assistance.
We understand that you need detailed steps about integrating SPA and SharePoint Server 2019, but unfortunately, Microsoft has not updated the article with new information about integrating SharePoint Server 2019 and SPA BO.
I only found articles in the SPA forum about integrating SharePoint 2016 and SPA BO. SharePoint Server 2016 is the most recent version of SharePoint with SharePoint 2019, so you can refer to this article to try to see if these steps are also suitable for SharePoint 2019.
Integration Option for Microsoft SharePoint Software Installation and Administration Guide
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
Since we have limited information and knowledge about SPA BO, it is highly suggested that you ask questions in the SPA Forum, perhaps you can get more specialized answers there.
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
However, if you find that these steps aren't being used or there are any issues with the process, the best way to resolve the issue further is to report it to the related team who has higher permission to access to more material and information and can investigate the issue from the back-end, collect the back-end logs, and help you find the root cause.
You may find phone number for your region accordingly from the link below:
Customer service phone numbers
The issue exceeds what we can handle right now owing to the rather limited resources. Please accept our sincerest apology for any inconvenience caused.
Certainty, if you have any concerns or questions, please do not hesitate to reach me. Please kindly note: we will always be standby to support you.
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