Error while trying to create a database for SSRS
I installed SQL Server 2017 side-by-side with an existing SQL Server 2014 instance. 

I installed SQL Server Reporting Services 2017 as per the download link. 

During the installation I was asked which edition of SSRS I would like to install. The options were:


Developer Edition
Evaluation Edition (180 days)
Express Edition


I selected Developer Edition and everything worked fine.



Mixed Editions

If I install the SSRS as an Express Edition, then the configuration of the SSRS datbase will fail with the mentioned error message: 



Solution

You have to install the SSRS 2017 using the same Edition as your SQL Server 2017 Edition. 


If you are running SQL Server 2017 Developer Edition then you have to install SQL Server 2017 Reporting Services with the option Developer Edition.
If you are running SQL Server 2017 Evaluation Edition then you have to install SQL Server 2017 Reporting Services with the option Evaluation Edition.
If you are running SQL Server 2017 Express Edition then you have to install SQL Server 2017 Reporting Services with the option Express Edition.


You will have to de-install your current SQL Server 2017 Reporting Services and ensure you install the identical Edition.



SSRS 2017 Developer Edition with SQL Server 2017 Developer Edition

I had no issues installing SSRS 2017 Developer Edition with SQL Server 2017 Developer Edition. 

SSRS Setup Step 1



SSRS Setup Step 2



SSRS Setup Step 3



SSRS Setup Step 4



SSRS Setup Step 5



SSRS Setup Step 6



SSRS Setup Step 7



If the editions match, then you won't have any issues. 
If the editions don't match, then you will encounter the error message.