You could use 'Assertion' Simulink block to create errors/ warnings when a certain condition is not met. You can have a look at the following example:
As illustrated in the figure below, an assertion failure occurs since the data '23' doesn't meet the required condition 'Data <= 20'.
You can mention the error/ warning message to be displayed in the block property as shown below:
You can also have a look at the following documentation page for more details on Assertion: Documentation.
Hope this helps!