If you are unable to make the connection to the SQL Express or SQL Server, check to see if the Windows Firewall is active. Right click on the Windows Logo in the lower left and select Search.

Please perform the following on the Computer that is hosting SQL Express or SQL Server.  You will need elevated permissions.

Click on Monitoring and check the status of the firewall. If the firewall is not active, skip down to step 19.

If active, now you are going to create an inbound rule for the SQL database and for SQL Browser. First, click on Inbound Rules at the top left and then New Rule at the top right.

Note, we do recommend checking your existing rules to verify there are no rules for the SQL database or SQL Browser that would conflict (advanced users only).

Select Program and then Next.

First, make a rule for the SQL Browser. Select the option for this program path and then navigate to the following location to select sqlbrowser.exe. Note, your shared directory will vary on the version of SQL you are running. Click Next to advance to the next screen.
Tip:  You may have multiple subfolders, you may want to check '90' first.
C:\Program Files (x86)\Microsoft SQL Server\xxx\Shared

Select Allow the connection and then Next.

Leave all of these checked and click Next.

Provide a name for the rule and then click Finish.

Now right click on the rule you just created and select Properties.

Select the Programs and Services tab and then Settings under the Services section.

Select Apply to services only and then OK.

Lastly, click Apply.

Now you are going to need to repeat steps 6 – 14. However, instead of pointing to the SQL Browser, you are now going to point to the SQL Server engine (sqlservr.exe). The following example shows you where the Treasury Software database is located.

Note, your MSSQL directory will vary on the version of SQL you are running.
Tips:
It will most likely be a different subfolder than used earlier - and under the C:\Program Files\ folder (not the C:\Program Files (x86)\)

As an example:
C:\Program Files\Microsoft SQL Server\MSSQL14.MSSQLSERVER\MSSQL\Binn\sqlservr.exe

Once you have created both the SQL Browser and SQL database rules, please enter back into the Treasury Software to try and make the connection to the database (Settings tab > Migrate to SQL Express, SQL Server).