Connection test for service RFC destination & unsuccessful

The connection test of the RFC destination for Web services failed.

What causes this issue?

The name of the given RFC destination for Web services is specified in
the central configuration. The destination is also configured in
transaction SM59. The destination has the required type 3 (ABAP
connections), but the test still failed.

System Response

A user with the type "Service" (complete with password) is a
prerequisite for a successful connection test.

How to fix this error?

Contact your system administrator and give him or her the number of the
error message.

Procedure for System Administrators

Check that the required RFC destination has been configured correctly.
Incorrect information about the user name in the RFC destination has
probably caused the connection test to fail. Call transaction SM59 and
select the given connection from the list of destinations of type 3
(ABAP connections). Run a connection test for this destination. If the
connection test fails, check the following:
Check whether the password for the user in the settings under "Logon &
Security" is correct.
Check whether the Unicode setting under "MDM" matches the system
information.
Check whether the character conversion settings for the destination are
correct.
Under "Special Options", check whether the qRFC version setting is set
to the classic qRFC version.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.