A form can prevent sending and show a message that does not help fix the problem. The person must know which field requires attention and how to correct it. The W3C tutorial on modules links instructions, validation, and notifications to the ability to complete the interaction in an accessible way.
I propose to write messages referring to the concrete problem, keeping the information already entered when appropriate. A generic formula on error can leave the user without a next action. Verification must include the relevant interaction modes, in addition to visual message reading.
Let's imagine a request that lacks a necessary data. The form should indicate the field and explain what information is needed, avoiding deleting the rest. A test with people who do not know the instrument can show points that the designer considers obvious.
The quality of the message can be read in the possibility of proceeding correctly. A useful control prevents unusable data and supports completion. The module becomes more understandable when it treats the error as a step to be solved, with a relevant explanation and a recognizable path for the reader.